WTNT44 KNHC 202317
TCDAT4
 
TROPICAL STORM IRENE SPECIAL DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
700 PM AST SAT AUG 20 2011
 
AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE
TROPICAL WAVE EAST OF THE LESSER ANTILLES FOUND A SMALL LOW-LEVEL
CIRCULATION CENTER JUST SOUTHWEST OF A LARGE CONVECTIVE BURST AND A
MINIMUM PRESSURE OF ABOUT 1006 MB.  THE PLANE ALSO MEASURED A
MAXIMUM WIND OF 53 KT AT 1400 FT AND BELIEVABLE WINDS OF ABOUT 
45 KT FROM THE SFMR.  THUS ADVISORIES ARE BEING INITIATED ON
TROPICAL STORM IRENE WITH AN INITIAL INTENSITY OF 45 KT.
 
A ROUGH ESTIMATE OF INITIAL MOTION IS ABOUT 280/19.  A LARGE
MID-LEVEL RIDGE OVER THE CENTRAL AND WESTERN TROPICAL ATLANTIC IS
EXPECTED TO STEER IRENE TOWARD THE WEST-NORTHWEST OVER THE NEXT TWO
OR THREE DAYS.  THIS RIDGE SHOULD WEAKEN DURING THAT TIME AND CAUSE
IRENE TO GRADUALLY DECELERATE.  THE GUIDANCE IS IN GOOD AGREEMENT 
ON A TRACK GENERALLY IN THE DIRECTION OF HISPANIOLA TO THE SOUTH OF
PUERTO RICO.  THEREAFTER...A MID-LATITUDE TROUGH MOVING OFFSHORE OF
THE EASTERN UNITED STATES IS EXPECTED TO CAUSE A WEAKNESS IN THE
RIDGE.  THIS COULD ALLOW IRENE TO GAIN SOME LATITUDE...ALTHOUGH THE
MODELS BEGIN TO SPREAD OUT LATE IN THE PERIOD.  THE GFS AND ECMWF
SHOW ENOUGH OF A WEAKNESS TO BRING THE STORM NORTH OF CUBA...WHILE
THE UKMET AND THE CANADIAN HAVE ENOUGH RIDGING IN PLACE TO KEEP THE
STORM IN THE CARIBBEAN SEA.  THE NHC FORECAST WILL SPLIT THOSE TWO
IDEAS AND LIES JUST TO THE WEST OF THE MODEL CONSENSUS.  
 
THE INITIAL VORTEX IS STILL IN ITS FORMATIVE STAGES AND IT WILL
PROBABLY TAKE SOME TIME TO STRENGTHEN.  HOWEVER...IRENE IS MOVING
OVER RATHER WARM WATERS WITH LIGHT SHEAR EXPECTED.   MOST OF THE
RELIABLE GUIDANCE BRINGS THE STORM TO A HURRICANE BEFORE REACHING
HISPANIOLA...AND THE OFFICIAL FORECAST IS IN AGREEMENT WITH THIS
SCENARIO.  THE INTENSITY FORECAST IN AT DAY 3 AND BEYOND IS RATHER
CHALLENGING DUE TO THE POTENTIAL FOR LAND INTERACTION.  ALTHOUGH
THE NHC FORECAST WILL SHOW ONLY A SMALL AMOUNT OF
RE-INTENSIFICATION...ENVIRONMENTAL CONDITIONS COULD BE QUITE
FAVORABLE FOR STRENGTHENING IF IRENE AVOIDS SIGNIFICANT LAND
INTERACTION.
 
BASED ON THE OFFICIAL FORECAST...TROPICAL STORM WARNINGS HAVE BEEN
ISSUED FOR MANY OF THE LEEWARD ISLANDS...THE VIRGIN ISLANDS AND
PUERTO RICO.  

NOTE...THIS SPECIAL ADVISORY TAKES THE PLACE OF THE STANDARD 800 PM
AST/0000 UTC INTERMEDIATE PUBLIC ADVISORY.  THE NEXT ADVISORY WILL
BE THE FULL ADVISORY PACKAGE ISSUED AT 1100 PM AST/0300 UTC. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  20/2300Z 14.9N  58.5W   45 KT  50 MPH
 12H  21/0600Z 15.4N  61.1W   45 KT  50 MPH
 24H  21/1800Z 16.1N  64.4W   50 KT  60 MPH
 36H  22/0600Z 16.7N  67.0W   55 KT  65 MPH
 48H  22/1800Z 17.5N  69.6W   65 KT  75 MPH
 72H  23/1800Z 19.0N  74.0W   45 KT  50 MPH
 96H  24/1800Z 21.5N  77.0W   45 KT  50 MPH
120H  25/1800Z 24.0N  79.5W   55 KT  65 MPH
 
$$
FORECASTER BLAKE/BRENNAN
 

WTNT44 KNHC 210252
TCDAT4
 
TROPICAL STORM IRENE DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 PM AST SAT AUG 20 2011

SATELLITE IMAGES INDICATE THAT IRENE IS MAINTAINING A LARGE AREA OF
CURVED CONVECTIVE BANDING ON THE NORTHERN SIDE OF THE SURFACE
CIRCULATION.  THE GUADELOUPE RADAR CONTINUES TO SHOW THIS BANDING
ALONG WITH A DISTINCT MID-LEVEL VORTEX...WHICH IS ALSO VISIBLE IN
MICROWAVE IMAGERY.  THE INITIAL WIND SPEED IS KEPT AT 45 KT AND THE
NEXT RECONNAISSANCE AIRCRAFT IS SCHEDULED TO FLY THROUGH IRENE
AROUND 1200 UTC.  
 
THE INITIAL MOTION ESTIMATE IS ABOUT 280/19.  A MID-LEVEL RIDGE OVER
THE WESTERN ATLANTIC OCEAN IS EXPECTED TO SLOWLY WEAKEN OVER THE
NEXT COUPLE OF DAYS.  THIS PATTERN SHOULD STEER IRENE TOWARD THE
WEST-NORTHWEST WITH A GRADUAL DECELERATION.  AFTER THAT TIME...A
MID-LATITUDE TROUGH MOVING OFFSHORE OF THE SOUTHEASTERN UNITED
STATES SHOULD CAUSE A WEAKNESS IN THE SUBTROPICAL RIDGE.  HOW MUCH
OF A WEAKNESS IS STILL UP FOR DEBATE...HOWEVER...WITH A VARIETY OF
MODEL SOLUTIONS SHOWING LARGE TRACK SPREAD AT THE END OF THE
FORECAST PERIOD.  IN ADDITION...A FEW OF THE MODELS...SUCH AS THE
UKMET...SHOW MORE OF AN EMPHASIS ON A SECOND TROUGH MOVING INTO THE
SOUTHERN UNITED STATES AND DO NOT SHOW THE FIRST TROUGH AFFECTING
IRENE MUCH.  THE GUIDANCE HAS SHIFTED SOMEWHAT TO THE WEST IN THE
LATER PERIODS...AND IT SEEMS REASONABLE TO SHIFT THE NHC FORECAST
IN THAT DIRECTION.  GIVEN THE LARGE SPREAD IN THE GUIDANCE...THIS IS
A GOOD TIME TO REMIND USERS THAT THE AVERAGE DAY 4 AND 5 NHC TRACK
FORECAST ERRORS ARE 200 TO 250 MILES.  

WITH THE IMPROVED STRUCTURE ON MICROWAVE...STRENGTHENING IS LIKELY
AS THE STORM TRAVERSES VERY WARM WATERS WITH LIGHT SHEAR
CONDITIONS.  ALMOST ALL OF THE GUIDANCE SHOWS IRENE BECOMING A
HURRICANE IN A DAY OR TWO...AND THE NHC FORECAST HAS BEEN INCREASED
DURING THE FIRST 48 HOURS. AFTER THAT TIME THE INTENSITY FORECAST
IS HIGHLY DEPENDENT ON HOW MUCH LAND INTERACTION OCCURS WITH
HISPANIOLA AND CUBA. THE CURRENT TRACK TAKES THE SYSTEM OVER THE
SPINE OF CUBA BETWEEN 72 AND 96 HOURS...SO LITTLE INTENSIFICATION
IS EXPECTED DURING THAT TIME...WITH SOME STRENGTHENING EXPECTED
NEAR THE END OF THE PERIOD AFTER IRENE MOVES AWAY FROM LAND. IT IS
WORTH NOTING THAT THE MODELS THAT SHOW LESS LAND INTERACTION...SUCH
AS THE GFDL OR HWRF...HAVE IRENE BECOMING A MAJOR HURRICANE...AND
THAT IS NOT OUT OF THE QUESTION ESPECIALLY IF THE STORM MOVES ON
THE FAR LEFT OR RIGHT SIDE OF THE FORECAST CONE AND AVOIDS
SIGNIFICANT LAND INTERACTION. OVERALL...GIVEN THE TRACK FORECAST
UNCERTAINTY AND THE POTENTIAL FOR LAND INTERACTION...THE INTENSITY
FORECAST LATE IN THE PERIOD IS EVEN MORE UNCERTAIN THAN USUAL. 

A HURRICANE WATCH COULD BE REQUIRED FOR PUERTO RICO TOMORROW IF
THERE IS A SIGNIFICANT NORTHWARD ADJUSTMENT TO THE TRACK FORECAST.

OF NOTE...THIS IS THE THIRD EARLIEST TO HAVE NINE NAMED STORMS FORM
IN THE ATLANTIC BASIN...BEHIND 2005 AND 1936.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/0300Z 15.3N  59.9W   45 KT  50 MPH
 12H  21/1200Z 16.0N  62.7W   50 KT  60 MPH
 24H  22/0000Z 16.6N  65.9W   55 KT  65 MPH
 36H  22/1200Z 17.2N  68.4W   65 KT  75 MPH
 48H  23/0000Z 18.0N  70.7W   75 KT  85 MPH
 72H  24/0000Z 19.5N  75.0W   50 KT  60 MPH
 96H  25/0000Z 21.5N  78.0W   50 KT  60 MPH...INLAND
120H  26/0000Z 24.5N  80.5W   60 KT  70 MPH...OVER WATER
 
$$
FORECASTER BLAKE/BRENNAN
 

WTNT44 KNHC 210859
TCDAT4
 
TROPICAL STORM IRENE DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 AM AST SUN AUG 21 2011
 
SATELLITE IMAGES AND RADAR DATA FROM GUADELOUPE INDICATE THAT IRENE
HAS CHANGED LITTLE IN THE PAST 6 HOURS. THE CENTER REDEVELOPED
ABOUT 60 NMI FARTHER NORTH INTO THE DEEP CONVECTION. HOWEVER...A
NARROW WEDGE OF DRY AIR HAS BEEN ENTRAINED INTO THE NORTHERN AND
WESTERN QUADRANTS...WHICH HAS ERODED SOME OF THE INNER CORE
CONVECTION NEAR THE LOW-LEVEL CENTER. AS A RESULT...THE INITIAL
INTENSITY REMAINS AT 45 KT...WHICH IS SUPPORTED BY A SATELLITE
INTENSITY ESTIMATE OF T3.0/45 KT FROM TAFB. THE NEXT HURRICANE
HUNTER AIRCRAFT SCHEDULED TO RECONNOITER IRENE WILL BE 1200 UTC.
 
THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 280/18 DUE TO THE
UNCERTAINTY IN THE INITIAL POSITION. 00Z UPPER-AIR DATA FROM THE
NORTHERN CARIBBEAN ISLANDS AND BERMUDA INDICATE A FAIRLY STOUT
DEEP-LAYER SUBTROPICAL RIDGE EXISTS TO THE NORTH AND NORTHWEST OF
IRENE. THE RESULTANT MODERATE EASTERLY STEERING FLOW SHOULD KEEP
THE CYCLONE MOVING IN A GENERAL WESTWARD TO WEST-NORTHWESTWARD
DIRECTION FOR THE NEXT 72 HOURS OR SO. AFTER THAT...A WEAKNESS IN
THE RIDGE IS EXPECTED TO DEVELOP ACROSS THE EASTERN GULF OF
MEXICO...FLORIDA...AND THE EXTREME WESTERN ATLANTIC...WHICH SHOULD
ALLOW IRENE TO TURN NORTHWESTWARD ACROSS HAITI AND EASTERN CUBA AND
EMERGE OVER THE FLORIDA STRAITS IN ABOUT 96 HOURS. ALL OF THE
MODELS ARE IN EXCELLENT AGREEMENT ON THIS DEVELOPING TRACK SCENARIO
EXCEPT FOR THE UKMET AND GFDL MODELS. THOSE LATTER TWO MODELS KEEP
IRENE ON A WESTERLY TRACK SOUTH OF CUBA AND THROUGH THE YUCATAN
CHANNEL...DESPITE THEIR DEVELOPING A SIMILAR BREAK IN THE RIDGE
AXIS OVER FLORIDA BY DAYS 4 AND 5...AND ARE CONSIDERED OUTLIERS AT
THIS TIME. THE OFFICIAL FORECAST TRACK IS NORTH OF THE PREVIOUS
ADVISORY TRACK MAINLY DUE TO THE MORE NORTHWARD INITIAL POSITION...
AND LIES CLOSE TO THE CONSENSUS MODELS TVCN AND TVCA.

THE UPPER-LEVEL ENVIRONMENT IS EXPECTED TO BE QUITE FAVORABLE FOR
STRENGTHENING THROUGHOUT THE FORECAST PERIOD AS A RESULT OF LOW
SHEAR AND A MID-OCEANIC TROUGH TO THE EAST ACTING AS A MASS SINK
FOR THE OUTFLOW IN THE EASTERN SEMICIRCLE. HOWEVER...THE INTENSITY
FORECAST IS HEAVILY DEPENDENT ON HOW MUCH INTERACTION IRENE HAS
WITH THE MOUNTAINOUS TERRAIN OF HISPANIOLA AND WHAT THE INNER CORE
OF THE CYCLONE BECOMES AFTER IT EMERGES OFF THE NORTHEAST COAST OF
CUBA IN ABOUT 4 DAYS. ONCE OVER THE FLORIDA STRAITS...HOWEVER...
IRENE WILL HAVE AT LEAST 24 HOURS OVER SOME OF THE WARMEST WATER IN
THE ATLANTIC TO TAP INTO. THE OFFICIAL FORECAST REMAINS ON THE
CONSERVATIVE SIDE DUE TO LAND EFFECTS AND IS CLOSE TO A BLEND OF
SHIPS AND LGEM STATISTICAL INTENSITY MODELS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/0900Z 16.4N  61.3W   45 KT  50 MPH
 12H  21/1800Z 17.0N  63.7W   50 KT  60 MPH
 24H  22/0600Z 17.5N  66.7W   60 KT  70 MPH
 36H  22/1800Z 18.0N  69.2W   70 KT  80 MPH
 48H  23/0600Z 18.6N  71.5W   50 KT  60 MPH...INLAND
 72H  24/0600Z 20.3N  75.3W   50 KT  60 MPH...INLAND
 96H  25/0600Z 22.8N  78.2W   60 KT  70 MPH...OVER WATER
120H  26/0600Z 26.1N  80.7W   75 KT  85 MPH...INLAND
 
$$
FORECASTER STEWART
 

WTNT44 KNHC 211457
TCDAT4
 
TROPICAL STORM IRENE DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 AM AST SUN AUG 21 2011
 
THE CLOUD PATTERN OF IRENE IS CHARACTERIZED BY WELL-DEFINED DEEP
CONVECTIVE BANDING FEATURES OVER THE NORTHERN SEMICIRCLE. THE STORM
STILL LACKS MUCH DEEP CONVECTION...OR STRONG WINDS...OVER THE
SOUTHERN PORTION OF THE CIRCULATION. AN AIR FORCE HURRICANE HUNTER
AIRCRAFT INVESTIGATING IRENE MEASURED PEAK 850 MB FLIGHT-LEVEL
WINDS OF 53 KT SO FAR...WHICH SUPPORTS KEEPING THE INTENSITY AT 45
KT FOR THIS ADVISORY. SINCE AN UPPER-LEVEL ANTICYCLONE IS
ESTABLISHED OVER THE TROPICAL CYCLONE AND THE SYSTEM WILL BE MOVING
OVER WARM WATERS...INTENSIFICATION SEEMS LIKELY AND IRENE IS
FORECAST TO BECOME A HURRICANE BY THE TIME IT REACHES HISPANIOLA.
AFTER THAT...THE INTENSITY FORECAST IS SUBJECT TO MORE THAN THE
USUAL LEVEL OF UNCERTAINTY...AS IT DEPENDS VERY MUCH ON HOW IRENE
WILL INTERACT WITH THE MOUNTAINOUS LAND MASSES OF HISPANIOLA AND
EASTERN CUBA OVER THE NEXT FEW DAYS. IF THE CENTER MOVES MORE OVER
THE WATER THAN INDICATED IN THE CURRENT FORECAST...IRENE WILL
LIKELY BECOME STRONGER THAN SHOWN HERE.

THE STORM IS BEING STEERED WEST-NORTHWESTWARD...285/17...BY THE FLOW
ON THE SOUTH SIDE OF A MID-LEVEL SUBTROPICAL RIDGE OVER THE WESTERN
ATLANTIC. OVER THE NEXT FEW DAYS...A COUPLE OF TROUGHS ARE FORECAST
TO CREATE A WEAKNESS IN THE RIDGE NEAR THE SOUTHEAST U.S.
COAST...WHICH SHOULD INDUCE A TURN TOWARD THE NORTHWEST. THERE IS A
FAIR AMOUNT OF SPREAD IN THE TRACK GUIDANCE MODELS...ESPECIALLY AT
DAYS 4 TO 5. FOR EXAMPLE...THE GFDL MODEL TAKES IRENE TO THE WEST
OF THE FLORIDA PENINSULA WHILE THE HWRF MODEL TAKES IT THROUGH THE
NORTHWESTERN BAHAMAS. INTERESTS IN FLORIDA ARE ADVISED NOT TO FOCUS
ON THE EXACT FORECAST TRACK BECAUSE OF THE INHERENT UNCERTAINTIES
IN LONGER-RANGE FORECASTS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/1500Z 17.0N  63.2W   45 KT  50 MPH
 12H  22/0000Z 17.5N  65.5W   55 KT  65 MPH
 24H  22/1200Z 18.2N  68.2W   65 KT  75 MPH
 36H  23/0000Z 18.9N  70.9W   50 KT  60 MPH...INLAND
 48H  23/1200Z 19.6N  73.3W   45 KT  50 MPH...INLAND
 72H  24/1200Z 21.5N  76.5W   50 KT  60 MPH...OVER WATER
 96H  25/1200Z 24.0N  79.0W   65 KT  75 MPH
120H  26/1200Z 27.0N  81.5W   50 KT  60 MPH...INLAND
 
$$
FORECASTER PASCH
 

WTNT44 KNHC 212045
TCDAT4
 
TROPICAL STORM IRENE DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 PM AST SUN AUG 21 2011
 
IRENE IS GRADUALLY BECOMING BETTER ORGANIZED IN ITS APPEARANCE ON
SATELLITE IMAGES...WITH CURVED BANDS BECOMING BETTER DEFINED.  THE
CURRENT INTENSITY IS HELD AT 45 KT IN ACCORDANCE WITH OBSERVATIONS
EARLIER THIS AFTERNOON FROM THE AIR FORCE HURRICANE HUNTERS.
ANOTHER HURRICANE HUNTER PLANE IS SCHEDULED TO INVESTIGATE IRENE
AROUND 0000 UTC.  WITH A WELL-DEFINED UPPER-LEVEL OUTFLOW
ANTICYCLONE SITUATED OVER THE STORM...THE PRIMARY IMPEDIMENT TO
STRENGTHENING OVER THE NEXT COUPLE OF DAYS SHOULD BE LAND
INTERACTION.  IF IRENE MOVES OVER MORE OF HISPANIOLA OR OVER PARTS
OF EASTERN CUBA IT WILL LIKELY BE WEAKER THAN INDICATED
HERE...HOWEVER IF THE SYSTEM ENDS UP MOVING TO THE NORTH OF BOTH OF
THOSE LAND MASSES IT COULD STRENGTHEN MORE THAN EXPECTED.  THE
OFFICIAL INTENSITY FORECAST IS SOMEWHAT HIGHER THAN THE LATEST LGEM
STATISTICAL-DYNAMICAL GUIDANCE.
 
THE FORWARD MOTION HAS SLOWED A BIT AND IS NOW NEAR 285/15.  IRENE
CONTINUES TO BE STEERED BY THE FLOW ON THE SOUTH SIDE OF A
MID-LEVEL SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC.  THE
WEST-NORTHWESTWARD MOTION IS LIKELY TO CONTINUE FOR 1 TO 2 DAYS
WHICH WOULD BRING THE CENTER NEAR OR OVER PUERTO RICO...AND NEAR OR
OVER THE DOMINICAN REPUBLIC.  OVER THE NEXT FEW DAYS...A COUPLE OF
TROUGHS ARE FORECAST TO CREATE A WEAKNESS IN THE RIDGE NEAR THE
SOUTHEAST U.S. COAST WHICH SHOULD INDUCE A TURN TO THE RIGHT AROUND
DAY 3.  SEVERAL OF THE RELIABLE TRACK GUIDANCE MODELS SUCH AS THE
ECMWF AND GFS HAVE SHIFTED EASTWARD FROM THEIR PREVIOUS RUNS AND SO
HAS THE DYNAMICAL CONSENSUS.  THE OFFICIAL TRACK FORECAST HAS BEEN
SHIFTED A LITTLE TO THE RIGHT OF THAT FROM THE PREVIOUS ADVISORY
AND LIES ON THE WESTERN SIDE OF THE GUIDANCE ENVELOPE.  IT IS
IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK...ESPECIALLY AT
DAYS 4 TO 5 SINCE THE MOST RECENT 5-YEAR AVERAGE ERRORS AT THOSE
FORECAST TIMES ARE 200 AND 250 MILES RESPECTIVELY.
   
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/2100Z 17.7N  64.4W   45 KT  50 MPH
 12H  22/0600Z 18.2N  66.6W   60 KT  70 MPH...INLAND
 24H  22/1800Z 18.9N  69.3W   65 KT  75 MPH...INLAND
 36H  23/0600Z 19.6N  71.5W   50 KT  60 MPH...INLAND
 48H  23/1800Z 20.3N  73.5W   50 KT  60 MPH...OVER WATER
 72H  24/1800Z 22.7N  76.7W   60 KT  70 MPH
 96H  25/1800Z 25.5N  79.5W   75 KT  85 MPH
120H  26/1800Z 28.5N  81.5W   50 KT  60 MPH...INLAND
 
$$
FORECASTER PASCH
 

WTNT44 KNHC 220259
TCDAT4
 
TROPICAL STORM IRENE DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 PM AST SUN AUG 21 2011
 
IRENE HAS CONTINUED TO BECOME BETTER ORGANIZED OVER THE PAST FEW
HOURS...AS THE CIRCULATION HAS BECOME BETTER DEFINED AND RADIAL
VELOCITIES HAVE INCREASED ON THE SAN JUAN DOPPLER RADAR. THERE HAS
ALSO BEEN A MARKED INCREASE IN DEEP CONVECTION NEAR THE CENTER ON
SATELLITE IMAGERY.  DATA FROM THE AIR FORCE RESERVE HURRICANE
HUNTER AIRCRAFT INDICATE THAT THE CENTRAL PRESSURE HAS FALLEN TO
993 MB.  THE INITIAL INTENSITY IS SET AT 60 KT BASED ON A PEAK
BELIEVABLE SFMR VALUE OF 61 KT AND AN EXPANDING AREA OF 65 TO 70 KT
DOPPLER VELOCITIES AT 5500 TO 6000 FEET ON THE SAN JUAN RADAR.
UPPER-LEVEL OUTFLOW IS WELL ESTABLISHED IN ALL QUADRANTS EXCEPT THE
SOUTHEAST AND ATMOSPHERIC AND OCEANIC CONDITIONS APPEAR FAVORABLE
FOR INTENSIFICATION...SO THE INTENSITY OF IRENE WILL LARGELY BE
DETERMINED BY HOW MUCH THE CYCLONE INTERACTS WITH LAND IN THE NEXT
24 TO 36 HOURS. SOME INTENSIFICATION IS STILL EXPECTED IN THE NEXT
FEW HOURS...AND IRENE COULD BECOME A HURRICANE BEFORE MOVING OVER
PUERTO RICO. THE CYCLONE IS THEN EXPECTED TO MOVE ACROSS THE
NORTHERN PORTION OF HISPANIOLA BETWEEN 24 AND 36 HOURS...AND SOME
WEAKENING IS INDICATED DURING THAT TIME. HOWEVER...IF IRENE MOVES
NORTH OF HISPANIOLA...IT COULD BE STRONGER THAN INDICATED HERE IN
36 TO 48 HOURS...OR WEAKER THAN FORECAST IF IT MOVES OVER MORE OF
THE HIGH TERRAIN OF THAT ISLAND. BEYOND 48 HOURS GRADUAL
STRENGTHENING IS EXPECTED AS IRENE MOVES OVER WARM WATERS NEAR THE
BAHAMAS...BUT THE UNCERTAINTY REMAINS VERY HIGH LATE IN THE PERIOD
DUE TO THE POTENTIAL FOR LAND INTERACTION IN THE SHORT TERM.
 
WHILE THE FORWARD MOTION OF THE CENTER APPEARED TO HAVE SLOWED ON
RADAR IMAGERY AS THE CYCLONE ORGANIZED DURING THE EVENING HOURS...
THE LONG TERM INITIAL MOTION ESTIMATE IS TOWARD 285 DEGREES AT ABOUT
13 KNOTS.  THE SUBTROPICAL RIDGE CURRENTLY SITUATED NORTH OF THE
CYCLONE WILL BREAK DOWN OVER THE NEXT DAY OR SO AS A LONGWAVE
MID-LEVEL TROUGH AMPLIFIES OVER THE WESTERN ATLANTIC.  THE TROUGH
BEGINS TO LIFT OUT AFTER ABOUT 36 HOURS OR SO...BUT LEAVES A
PRONOUNCED WEAKNESS IN THE RIDGE OVER THE SOUTHWESTERN ATLANTIC AND
THE BAHAMAS.  MOST OF THE GUIDANCE...WITH THE EXCEPTION OF THE GFDL
AND UKMET...ARE IN RELATIVELY GOOD AGREEMENT ON TURNING IRENE
NORTHWESTWARD INTO THE BREAK IN THE RIDGE IN 2 OR 3 DAYS. 
HOWEVER...SIGNIFICANT SPREAD REMAINS IN THE SHARPNESS OF THIS TURN
IN THE MODEL SUITE.  FOR THIS CYCLE THE CONSENSUS TRACK MODELS HAVE
SHIFTED BACK A LITTLE TO THE LEFT...WITH THE GFS...ECMWF...AND HWRF
MODELS ON THE EAST SIDE OF THE GUIDANCE ENVELOPE AND THE
AFOREMENTIONED UKMET AND GFDL FARTHER WEST.  THE OFFICIAL FORECAST
HAS BEEN NUDGED TO THE RIGHT...TOWARD BUT STILL TO THE LEFT OF THE
MODEL CONSENSUS...AND LIES CLOSE TO THE FIM MODEL PROVIDED BY THE
HURRICANE FORECAST IMPROVEMENT PROJECT.  

IT IS IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK...
ESPECIALLY AT DAYS 4 TO 5...SINCE THE MOST RECENT 5-YEAR AVERAGE
ERRORS AT THOSE FORECAST TIMES ARE 200 AND 250 MILES...
RESPECTIVELY.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  22/0300Z 17.9N  65.5W   60 KT  70 MPH
 12H  22/1200Z 18.6N  67.7W   60 KT  70 MPH
 24H  23/0000Z 19.4N  70.1W   60 KT  70 MPH...INLAND
 36H  23/1200Z 20.1N  72.1W   50 KT  60 MPH...OVER WATER
 48H  24/0000Z 20.9N  73.9W   55 KT  65 MPH
 72H  25/0000Z 23.5N  77.0W   65 KT  75 MPH
 96H  26/0000Z 26.5N  79.5W   80 KT  90 MPH
120H  27/0000Z 30.0N  81.5W   75 KT  85 MPH...INLAND
 
$$
FORECASTER BRENNAN
 

WTNT44 KNHC 220859
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 AM AST MON AUG 22 2011
 
IRENE HAS BECOME MUCH BETTER ORGANIZED DURING THE PAST 6 HOURS
DESPITE ITS INTERACTION WITH THE MOUNTAINOUS TERRAIN OF PUERTO
RICO...AND A RAGGED EYE HAS BECOME APPARENT IN IMAGERY FROM THE FAA
TERMINAL DOPPLER WEATHER RADAR. ALSO...LARGE PATCHES OF DOPPLER
VELOCITY VALUES AS HIGH AS 75-82 KT AT 1000-1500 FT AND 85-91 KT 
AT 2000-3000 FT HAVE BEEN INDICATED NORTHWEST AND NORTHEAST OF THE
CENTER OVER WATER FOR THE PAST 2 HOURS...WHICH EQUATES TO AT LEAST
65-KT SURFACE WINDS. SOME DOPPLER VELOCITIES AS HIGH AS 72 KT HAVE
ALSO BEEN DETECTED AT 500-600 FT OVER WATER. AS A RESULT OF THESE
DATA...IRENE HAS BEEN UPGRADED TO THE FIRST HURRICANE OF THE 2011
ATLANTIC HURRICANE SEASON.

TRENDING THROUGH ALL OF THE WOBBLES IN THE TRACK OVER THE PAST 6
HOURS YIELDS AN AVERAGE MOTION OF ABOUT 290/10 KT. UPPER-AIR DATA
AT 00Z INDICATE 500 MB HEIGHTS HAVE NOT CHANGED AT BERMUDA IN THE
PAST 24 HOURS...WHICH SUGGESTS THAT THE SUBTROPICAL RIDGE TO THE
NORTH OF IRENE REMAINS QUITE STRONG. THE RIDGE IS EXPECTED TO
CHANGE LITTLE FOR THE NEXT 48 HOURS OR SO...WHICH WOULD ACT TO KEEP
IRENE MOVING IN A GENERAL WEST-NORTHWESTWARD DIRECTION OFF THE
NORTH COAST OF PUERTO RICO THIS MORNING AND JUST SKIRTING THE
NORTHERN COAST OF HISPANIOLA LATER TODAY AND ON TUESDAY. AFTER
THAT...THE GLOBAL MODELS DIVERGE ON THE SPECIFICS OF HOW LARGE A
BREAK OR WEAKNESS IN THE SUBTROPICAL RIDGE DEVELOPS OVER FLORIDA
AND THE SOUTHEASTERN U.S. AT 72 HOUR AND BEYOND...WHICH WILL ALLOW
IRENE TO MOVE NORTHWESTWARD. THE ECMWF...NOGAPS...AND GFDN MODELS
ARE THE RIGHTMOST OF THE NHC MODEL GUIDANCE SUITE AND KEEP IRENE
WELL EAST OF FLORIDA...WHEREAS THE UKMET AND THE GFDL MODELS ARE
THE LEFTMOST OF THE MODELS AND TAKE IRENE NEAR THE WEST COAST OF
FLORIDA. THE GFS AND THE REST OF THE NHC MODEL GUIDANCE IS TIGHTLY
PACKED BETWEEN THESE TWO EXTREMES AND TAKE IRENE THROUGH THE
BAHAMAS AND JUST OFF THE FLORIDA EAST COAST. WHAT IS NOTEWORTHY IS
THAT ALL OF THE GLOBAL AND REGIONAL MODELS AGREE THAT THE OUTFLOW
OF IRENE WILL CONVERGE WITH WESTERLY TO NORTHWESTERLY UPPER-LEVEL
MID-LATITUDE FLOW OVER THE MID-ATLANTIC STATES BY 96 HOURS AND
BEYOND. THIS UPPER-LEVEL MASS CONFLUENCE COULD MAINTAIN THE MID- TO
LOW-LEVEL RIDGE A LITTLE BIT STRONGER AND LONGER THAN WHAT NOGAPS
AND THE ECMWF ARE FORECASTING...WHICH WOULD IN TURN KEEP IRENE A
LITTLE CLOSER TO THE FLORIDA EAST COAST. AS A RESULT...THE OFFICIAL
FORECAST TRACK WAS ONLY SHIFTED SLIGHTLY TO THE EAST OF THE
PREVIOUS TRACK AND IS NEAR THE CONSENSUS MODELS TVCN AND TVCA.

IT NOW APPEARS THAT IRENE WILL NOT INTERACT WITH HISPANIOLA AS MUCH
OR AS LONG AS PREVIOUSLY EXPECTED. THIS WILL ALSO RESULT IN MORE
STRENGTHENING THAN PREVIOUSLY EXPECTED. IRENE IS FORECAST BY ALL OF
THE MODELS TO HAVE A VERY IMPRESSIVE OUTFLOW PATTERN THROUGHOUT THE
FORECAST PERIOD...INCLUDING A LARGE UPPER-LEVEL TROUGH/LOW ABOUT
1200 NMI EAST OF THE CYCLONE ACTING AS A MASS SINK. WITH IRENE ALSO
EXPECTED TO BE OVER SSTS NEAR 30C AFTER 48 HOURS...SIGNIFICANT
STRENGTHENING COULD OCCUR. HOWEVER...THE OFFICIAL INTENSITY WILL
REMAIN ON THE CONSERVATIVE SIDE DUE TO THE UNCERTAINTY IN HOW MUCH
IRENE WILL INTERACT WITH THE MOUNTAINOUS TERRAIN OF HISPANIOLA FOR
THE NEXT 24-36 HOURS. THE OFFICIAL INTENSITY FORECAST IS A BLEND OF
THE SHIPS/LGEM MODELS AND THE HWRF/GFDL MODELS. HOWEVER...GIVEN THE
IMPRESSIVE UPPER-LEVEL FLOW PATTERN EXPECTED ACROSS IRENE...IT
WOULD NOT SURPRISE ME IF THIS CYCLONE BECAME A MAJOR HURRICANE AT
SOME TIME DURING ITS LIFETIME LIKE THE GFDL AND HWRF MODELS ARE
FORECASTING.

IT IS IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK...
ESPECIALLY AT DAYS 4 TO 5...SINCE THE MOST RECENT 5-YEAR AVERAGE
ERRORS AT THOSE FORECAST TIMES ARE 200 AND 250 MILES...
RESPECTIVELY.

FORECAST POSITIONS AND MAX WINDS
 
INIT  22/0900Z 18.4N  66.4W   65 KT  75 MPH
 12H  22/1800Z 18.9N  68.2W   70 KT  80 MPH
 24H  23/0600Z 19.7N  70.5W   70 KT  80 MPH...INLAND
 36H  23/1800Z 20.4N  72.4W   70 KT  80 MPH...OVER WATER
 48H  24/0600Z 21.3N  74.1W   75 KT  85 MPH
 72H  25/0600Z 24.0N  77.1W   80 KT  90 MPH
 96H  26/0600Z 27.0N  79.5W   85 KT 100 MPH
120H  27/0600Z 30.9N  81.5W   95 KT 110 MPH
 
$$
FORECASTER STEWART
 

WTNT44 KNHC 221504
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 AM AST MON AUG 22 2011
 
DATA FROM A RECONNAISSANCE PLANE...RADAR AND SATELLITE IMAGERY
INDICATE THAT IRENE HAS CONTINUED TO GRADUALLY BECOME BETTER
ORGANIZED. HOWEVER THE WINDS WINDS HAVE NOT INCREASED SIGNIFICANTLY
AND THE MINIMUM CENTRAL PRESSURE WAS AROUND 988 MB IN THE LAST
CENTER DROPSONDE. THE INITIAL INTENSITY HAS BEEN INCREASED TO 70
KNOTS IN THIS ADVISORY. SINCE THE CORE OF THE HURRICANE IS NOT
FORECAST TO MOVE DIRECTLY OVER THE HIGH TERRAIN OF HISPANIOLA...AND
THE OCEANIC AND ATMOSPHERIC CONDITIONS ARE QUITE FAVORABLE... THE
OFFICIAL FORECAST CALLS FOR INTENSIFICATION...AND MAKES IRENE A
CATEGORY 3 HURRICANE AS IT MOVES ACROSS THE CENTRAL BAHAMAS. THIS
IS CONSISTENT WITH MOST OF THE DYNAMICAL GUIDANCE AND IN
FACT...EVEN GLOBAL MODELS FORECAST A SIGNIFICANT DROP IN THE
CENTRAL PRESSURE OVER THE NEXT TWO OR THREE DAYS. IRENE IS BECOMING
A LARGE CYCLONE...AND BASED ON BUOY OBSERVATIONS THE TROPICAL STORM
FORCE WINDS EXTEND 160 N MI TO THE NORTHEAST OF THE CENTER.
 
RADAR AND RECONNAISSANCE FIXES INDICATE THAT THE HURRICANE IS MOVING
TOWARD THE WEST-NORTHWEST OR 295 DEGREES AT ABOUT 12 KNOTS. IRENE
IS CURRENTLY LOCATED SOUTH OF A NARROW SUBTROPICAL RIDGE WHICH IS
FORCING THE CYCLONE ON A WEST-NORTHWEST TRACK. HOWEVER...MOST OF
THE GLOBAL MODELS SHOW THE GRADUAL DEVELOPMENT A LARGE UPPER TROUGH
ALONG THE UNITED STATES EAST COAST. THIS PATTERN WILL INDUCE A MORE
NORTHWESTWARD AND THEN NORTHWARD TRACK THROUGH THE FORECAST PERIOD
WITH A DECREASE IN FORWARD SPEED. BASED ON THE LATEST GUIDANCE...
THE OFFICIAL TRACK FORECAST HAS BEEN SHIFTED TO THE EAST...BUT
STILL REMAINS SLIGHTLY WEST OF THE MODEL CONSENSUS. ALTHOUGH IT IS
TOO EARLY TO BE CERTAIN...THE CURRENT GUIDANCE LESSENS THE THREAT
TO SOUTH FLORIDA.
 
DO NOT TO FOCUS ON THE EXACT FORECAST TRACK...ESPECIALLY AT DAYS 4
TO 5...SINCE THE MOST RECENT 5-YEAR AVERAGE ERRORS AT THOSE
FORECAST TIMES ARE 200 AND 250 MILES...RESPECTIVELY.
 
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  22/1500Z 19.2N  67.5W   70 KT  80 MPH
 12H  23/0000Z 19.9N  69.2W   75 KT  85 MPH
 24H  23/1200Z 20.5N  71.4W   80 KT  90 MPH
 36H  24/0000Z 21.2N  73.2W   85 KT 100 MPH
 48H  24/1200Z 22.0N  75.0W   90 KT 105 MPH
 72H  25/1200Z 25.0N  77.5W  100 KT 115 MPH
 96H  26/1200Z 28.5N  79.0W  100 KT 115 MPH
120H  27/1200Z 32.5N  80.0W  100 KT 115 MPH
 
$$
FORECASTER AVILA
 

WTNT44 KNHC 222052
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 PM AST MON AUG 22 2011
 
DATA FROM THE LAST AIR FORCE HURRICANE HUNTER AIRCRAFT AROUND 1700
UTC INDICATE THAT THE CENTRAL PRESSURE WAS STEADY AND THE WINDS
HAVE NOT CHANGED DURING THE DAY. SINCE THEN...HIGH RESOLUTION
SATELLITE IMAGES REVEAL SOME CONVECTIVE BANDS WRAPPING AROUND A
CLUSTER OF DEEP CONVECTION NEAR THE CENTER...SUGGESTING THAT IRENE
COULD BE SLOWLY INTENSIFYING. HOWEVER...DVORAK T-NUMBERS ARE 4.0
AND 4.5 WHICH SUPPORTS KEEPING THE INITIAL INTENSITY AT 70 KNOTS.
ANOTHER PLANE WILL CHECK THE HURRICANE AROUND 0000 UTC TONIGHT.
WITH THE EXCEPTION OF THE DISRUPTION OF THE OUTER CIRCULATION BY
THE HIGH TERRAIN OF HISPANIOLA...WHICH PROBABLY WILL SLOW DOWN THE
INTENSIFICATION PROCESS DURING THE NEXT 12 TO 24 HOURS...ALL OF THE
INGREDIENTS ARE CONDUCIVE FOR IRENE TO INTENSIFY OVER THE NEXT FEW
DAYS. THE OFFICIAL FORECAST CALLS FOR IRENE TO BECOME A STRONG
CATEGORY 2 OR CATEGORY 3 HURRICANE ON THE SAFFIR-SIMPSON HURRICANE
WIND SCALE AS IRENE MOVES ACROSS THE CENTRAL AND NORTHWESTERN
BAHAMAS. IN FACT...BOTH THE GFS AND THE ECMWF GLOBAL MODELS INSIST
ON MAKING IRENE A LARGE AND STRONG HURRICANE WITH MINIMUM PRESSURES
AROUND 945 MB AND 952 MB...RESPECTIVELY.  

IRENE IS MOVING TOWARD THE WEST-NORTHWEST OR 295 DEGREES AT 11
KNOTS. CURRENTLY...THE MOTION OF THE HURRICANE IS BEING CONTROLLED
BY A NARROW SUBTROPICAL RIDGE TO ITS NORTH. HOWEVER...THE FUTURE
TRACK WILL DEPEND ON THE DEVELOPMENT OF A LARGE MID- TO UPPER-LEVEL
TROUGH ALONG THE EAST COAST OF THE UNITED STATES. THIS PATTERN WILL
INDUCE A GRADUAL NORTHWESTWARD AND THEN NORTHWARD TRACK THROUGH THE
FORECAST PERIOD WITH A SLIGHT DECREASE IN FORWARD SPEED. THERE IS
MORE CONFIDENCE IN THE FORECAST SINCE MOST OF THE TRACK MODELS...
WITH THE EXCEPTION OF THE GFDL...HAVE NOW FOLLOWED THE LEAD OF THE
ECMWF MODEL. THE GUIDANCE IS NOW IN BETTER AGREEMENT IN TURNING
IRENE NORTHWARD ALONG 78 OR 79 DEGREES LONGITUDE. ALTHOUGH IT IS
STILL TOO EARLY TO BE CERTAIN...THE GUIDANCE TREND CONTINUES TO
LESSENS THE THREAT TO SOUTH FLORIDA BUT INCREASES THE THREAT TO THE
CAROLINAS. 
 
DO NOT TO FOCUS ON THE EXACT FORECAST TRACK...ESPECIALLY AT DAYS 4
TO 5...SINCE THE MOST RECENT 5-YEAR AVERAGE ERRORS AT THOSE FORECAST
TIMES ARE 200 AND 250 MILES...RESPECTIVELY.
 

FORECAST POSITIONS AND MAX WINDS
 
INIT  22/2100Z 19.5N  68.6W   70 KT  80 MPH
 12H  23/0600Z 20.1N  70.2W   80 KT  90 MPH
 24H  23/1800Z 20.8N  72.5W   85 KT 100 MPH
 36H  24/0600Z 21.5N  74.0W   90 KT 105 MPH
 48H  24/1800Z 23.0N  75.5W   95 KT 110 MPH
 72H  25/1800Z 26.0N  78.0W  100 KT 115 MPH
 96H  26/1800Z 29.5N  79.0W  100 KT 115 MPH
120H  27/1800Z 34.0N  79.0W   80 KT  90 MPH...INLAND
 
$$
FORECASTER AVILA
 

WTNT44 KNHC 230029
TCDAT4
 
HURRICANE IRENE SPECIAL DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
830 PM AST MON AUG 22 2011

THE HURRICANE HUNTER AIRCRAFT FOUND A 850-MB FLIGHT LEVEL WIND
MAXIMUM OF 106 KT ON ITS FIRST PASS THROUGH THE CENTER OF IRENE.
BASED ON THIS...THE INITIAL INTENSITY IS ADJUSTED UPWARD TO 85 KT.
OVER THE PAST COUPLE OF HOURS THE SATELLITE PRESENTATION OF THE
HURRICANE HAS CONTINUED TO IMPROVE...ALTHOUGH NO EYE IS VISIBLE YET
IN GEOSTATIONARY IMAGERY. HOWEVER...AN EYE HAS BECOME APPARENT ON
THE SAN JUAN DOPPLER RADAR AND WAS ALSO SEEN IN A 2230 UTC SSMIS
PASS. THE CENTRAL PRESSURE HAS FALLEN TO 981 MB BASED ON A
DROPSONDE OBSERVATION OF 982 MB WITH 10 KT OF WIND AT THE SURFACE.
GIVEN THAT THE ENVIRONMENT APPEARS CONDUCIVE FOR ADDITIONAL
STRENGTHENING...THE INTENSITY FORECAST HAS BEEN ADJUSTED UPWARD BY
15 KT THROUGH 36 HOURS WITH A SMALLER UPWARD ADJUSTMENT AT 48 AND
72 HOURS. ONLY SLIGHT WEAKENING IS INDICATED AT DAYS 4 AND 5. THE
NEW FORECAST NOW SHOWS IRENE BECOMING A MAJOR HURRICANE ON TUESDAY
AS IT MOVES THROUGH THE SOUTHEASTERN BAHAMAS AND THE TURKS AND
CAICOS ISLANDS. THE WIND RADII HAVE BEEN EXPANDED BASED ON AIRCRAFT
DATA AND THE NEW INTENSITY FORECAST.

NO CHANGES HAVE BEEN MADE TO THE TRACK FORECAST ON THIS SPECIAL
ADVISORY. 
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/0030Z 19.7N  68.7W   85 KT 100 MPH
 12H  23/0600Z 20.1N  70.2W   95 KT 110 MPH
 24H  23/1800Z 20.8N  72.5W  105 KT 120 MPH
 36H  24/0600Z 21.5N  74.0W  110 KT 125 MPH
 48H  24/1800Z 23.0N  75.5W  110 KT 125 MPH
 72H  25/1800Z 26.0N  78.0W  110 KT 125 MPH
 96H  26/1800Z 29.5N  79.0W  105 KT 120 MPH
120H  27/1800Z 34.0N  79.0W   95 KT 110 MPH...INLAND
 
$$
FORECASTER BRENNAN
 

WTNT44 KNHC 230300
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 PM AST MON AUG 22 2011
 
AFTER DEEPENING QUICKLY EARLIER THIS EVENING...THE INTENSITY OF
IRENE APPEARS TO HAVE LEVELED OFF A BIT OVER THE PAST HOUR OR TWO.
THE CENTRAL PRESSURE HAS DECREASED TO 980 MB ...AND MAXIMUM WINDS
HAVE NOT INCREASED SINCE THE EARLIER MAXIMUM OF 106 KT AT 850 MB.
THEREFORE...THE INTENSITY WILL REMAIN 85 KT FOR THIS ADVISORY.
OVERALL THE STRUCTURE OF THE CYCLONE HAS CONTINUED TO IMPROVE...
WITH A LARGE CDO FORMING NEAR AND NORTH OF THE CENTER AND THE
AIRCRAFT REPORTING A CLOSED EYEWALL.  SOUTHERLY SHEAR OF ABOUT 10
KT IS PRESENT OVER IRENE ACCORDING TO SATELLITE ANALYSIS FROM
UW-CIMSS AND THE SHIPS MODEL...BUT OTHERWISE THE ENVIRONMENT
APPEARS CONDUCIVE FOR CONTINUED STRENGTHENING.  THE NHC INTENSITY
FORECAST IS UNCHANGED FROM THE PREVIOUS SPECIAL ADVISORY AND SHOWS
IRENE BECOMING A MAJOR HURRICANE WITHIN 24 HOURS AND REACHING A
PEAK OF 115 KT IN 72 HOURS...FOLLOWED BY SLOW WEAKENING LATE IN THE
PERIOD.  THE NHC FORECAST IS HIGHER THAN MOST OF THE GUIDANCE
THROUGH 48 HOURS AND IS CLOSE TO A BLEND OF THE GFDL AND HWRF
MODELS AFTER THAT TIME.
 
AIRCRAFT FIXES INDICATE THAT THE CENTER WAS LOCATED A LITTLE TO THE
RIGHT OF THE PREVIOUS TRACK AND THAT THE FORWARD MOTION HAS SLOWED
A BIT...WITH AN INITIAL MOTION ESTIMATE OF 295/10. OVERALL THE
TRACK FORECAST SCENARIO HAS NOT CHANGED...AS IRENE WILL CONTINUE
MOVING WEST-NORTHWESTWARD FOR THE NEXT DAY OR SO ON THE SOUTHWEST
PERIPHERY OF A WEAKENING MID-LEVEL RIDGE. A MID- TO UPPER-LEVEL
TROUGH LOCATED EAST OF NORTH AMERICA WILL LIFT OUT WITHIN 24
HOURS...LEAVING A PRONOUNCED WEAKNESS IN THE RIDGE OVER THE
BAHAMAS.  THIS SHOULD ALLOW IRENE TO GRADUALLY TURN NORTHWESTWARD
AND NORTH-NORTHWESTWARD BY DAYS 2 AND 3.  AFTER THAT TIME...THE
TRACK OF IRENE APPEARS TO BE SENSITIVE TO THE TIMING AND AMPLITUDE
OF SEVERAL SHORTWAVE TROUGHS MOVING EASTWARD ACROSS THE UNITED
STATES/CANADIAN BORDER. THE MODELS ARE SHOWING SOME RUN-TO-RUN
VARIABILITY IN HOW MUCH THESE SHORTWAVES WILL AMPLIFY AND DEEPEN
THE MEAN TROUGH OVER THE NORTHEASTERN UNITED STATES...WHICH WILL BE
CRITICAL TO HOW SOON IRENE TURNS NORTHWARD OR EVEN EAST OF DUE
NORTH AT DAYS 4 AND 5. OVERALL...THE SPREAD OF THE GUIDANCE SUITE
HAS DECREASED THIS CYCLE...AND THE COMBINATION OF THE SLIGHT
RIGHTWARD ADJUSTMENT OF THE INITIAL POSITION AND A SLIGHT WESTWARD
SHIFT IN THE MODEL CONSENSUS RESULTS IN ONLY MINOR ADJUSTMENTS TO
THE NEW NHC TRACK FORECAST. THE BIGGEST CHANGE IS A SLOWER FORWARD 
SPEED AT THE END OF THE PERIOD FOLLOWING THE BULK OF THE GUIDANCE
THAT KEEPS THE CYCLONE OFFSHORE AT DAY 5.
 
IT IS IMPORTANT TO REMIND USERS NOT TO FOCUS ON THE EXACT FORECAST
TRACK...ESPECIALLY AT DAYS 4 AND 5...SINCE THE MOST RECENT 5-YEAR
AVERAGE ERRORS AT THOSE FORECAST TIMES ARE 200 AND 250 MILES...
RESPECTIVELY.
 
OF NOTE...SYNOPTIC SURVEILLANCE FLIGHTS FROM THE NOAA G-IV AND AN
AIR FORCE RESERVE C-130 AIRCRAFT PROVIDED NUMEROUS DROPSONDES FOR
ASSIMILATION INTO THE 0000 UTC MODEL CYCLE.  THIS SHOULD IMPROVE
THE ANALYSIS OF THE ENVIRONMENT AROUND AND UPSTREAM OF IRENE.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/0300Z 19.9N  69.2W   85 KT 100 MPH
 12H  23/1200Z 20.4N  70.6W   95 KT 110 MPH
 24H  24/0000Z 21.1N  72.4W  105 KT 120 MPH
 36H  24/1200Z 22.2N  74.2W  110 KT 125 MPH
 48H  25/0000Z 23.5N  75.6W  110 KT 125 MPH
 72H  26/0000Z 26.5N  78.0W  115 KT 135 MPH
 96H  27/0000Z 30.0N  79.0W  105 KT 120 MPH
120H  28/0000Z 33.5N  78.5W  100 KT 115 MPH
 
$$
FORECASTER BRENNAN
 

WTNT44 KNHC 230838
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  12
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 AM EDT TUE AUG 23 2011
 
SMOOTHING THROUGH ALL OF THE AIRCRAFT FIXES SINCE IRENE MOVED OFF
THE COAST OF PUERTO RICO MORE THAN 18 HOURS AGO YIELDS A LONG TERM
MOTION OF 295/10 KT...WHICH IS USED FOR THIS ADVISORY. THERE IS NO
SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK REASONING. THE
23/00Z G-IV JET AIRCRAFT AND AIR FORCE C-130 DROPSONDE DATA APPEAR
TO HAVE SETTLED DOWN THE MODELS...AND THERE IS CONSIDERABLY LESS
DIFFERENCE AMONG THE VARIOUS MODEL SOLUTIONS NOW. THE OVERWHELMING
CONSENSUS IS THAT IRENE WILL GRADUALLY TURN NORTHWESTWARD OVER THE
NEXT 2-3 DAYS AND THEN MOVE NORTHWARD THROUGH A DEVELOPING BREAK IN
THE SUBTROPICAL RIDGE OVER THE SOUTHEASTERN UNITED STATES. THE
OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND
LIES VERY CLOSE TO CONSENSUS MODELS TVCN AND TVCA.
 
AN EARLIER RECON FLIGHT INDICATED THE PRESSURE HAD ONLY FALLEN BY 2
MB DOWN TO 978 MB...AND THE OVERALL APPEARANCE IN SATELLITE IMAGERY
HAS CHANGED LITTLE SINCE THE PREVIOUS ADVISORY. AS A RESULT...THE
INITIAL INTENSITY IS BEING HELD AT 85 KT...WHICH COULD BE GENEROUS.
IRENE IS FORECAST TO REMAIN IN A RELATIVELY LOW VERTICAL WIND SHEAR
ENVIRONMENT AND OVER SSTS NEAR 30C. THAT COMBINATION...ALONG WITH
EXPANDING OUTFLOW IN ALL QUADRANTS...SHOULD ALLOW FOR IRENE TO
BECOME A MAJOR HURRICANE WITHIN THE NEXT 24 HOURS ONCE THE CYCLONE
CLEARS THE EFFECTS OF HISPANIOLA...AND PROBABLY MAINTAIN MAJOR
HURRICANE STATUS THROUGHOUT THE REMAINDER OF THE 5-DAY FORECAST
PERIOD. THE INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY
AND CLOSELY FOLLOWS A BLEND OF THE HWRF AND GFDL MODEL INTENSITY
FORECASTS...AND CONVERSION OF THE SURFACE PRESSURES DEPICTED IN THE
GFS AND ECMWF MODELS.
 
WIND RADII WERE EXPANDED BASED ON A BLEND OF RECON FLIGHT-LEVEL
WINDS...SFMR WINDS...AND SURFACE OBSERVATIONS.
 
IRENE IS FORECAST TO BECOME A LARGER THAN AVERAGE HURRICANE. IT IS
IMPORTANT TO REMIND USERS NOT TO FOCUS ON THE EXACT FORECAST
TRACK...ESPECIALLY AT DAYS 4 AND 5...SINCE THE MOST RECENT 5-YEAR
AVERAGE ERRORS AT THOSE FORECAST TIMES ARE 200 AND 250 MILES...
RESPECTIVELY.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/0900Z 20.3N  70.1W   85 KT 100 MPH
 12H  23/1800Z 20.9N  71.5W   95 KT 110 MPH
 24H  24/0600Z 21.7N  73.3W  105 KT 120 MPH
 36H  24/1800Z 22.9N  74.9W  110 KT 125 MPH
 48H  25/0600Z 24.3N  76.2W  110 KT 125 MPH
 72H  26/0600Z 28.0N  78.0W  115 KT 135 MPH
 96H  27/0600Z 31.5N  78.3W  105 KT 120 MPH
120H  28/0600Z 35.0N  78.0W  100 KT 115 MPH...INLAND
 
$$
FORECASTER STEWART
 

WTNT44 KNHC 231500
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 AM EDT TUE AUG 23 2011
 
THE LAST FEW VISIBLE SATELLITE IMAGES SHOW A HINT OF AN EYE... WHILE
RECENT MICROWAVE DATA SHOW AN EYEWALL THAT IS OPEN TO THE SOUTH.
THE LATEST SATELLITE INTENSITY ESTIMATES FROM SAB AND TAFB WERE 77
AND 90 KT...RESPECTIVELY...AND SUPPORT MAINTAINING AN INITIAL
INTENSITY OF 85 KT. THE RECONNAISSANCE AIRCRAFT SCHEDULED TO
INVESTIGATE IRENE THIS MORNING HAD ISSUES WITH THE ON-BOARD RADAR.
THIS REQUIRED A CHANGE IN AIRCRAFT AND THE NEW PLANE JUST PASSED
THROUGH THE CENTER...REPORTING A MINIMUM PRESSURE OF 980 MB...ABOUT
THE SAME AS DURING THE PREVIOUS MISSION.
 
A SHEAR ANALYSIS FROM UW-CIMSS SHOWS ABOUT 10-20 KT OF SOUTHWESTERLY
SHEAR OVER IRENE....AND THE SHIPS GUIDANCE DOES NOT WEAKEN THIS
SHEAR DURING THE NEXT COUPLE OF DAYS.  AS A RESULT...THE SHIPS/LGEM
MODELS DO NOT SHOW MUCH STRENGTHENING DURING THAT TIME.  ON THE
OTHER HAND...THE GFDL/HWRF MODELS ARE MUCH MORE AGGRESSIVE AND MAKE
IRENE A MAJOR HURRICANE WITHIN 24 HOURS. THE NEW INTENSITY FORECAST
IS HIGHER THAN THE STATISTICAL GUIDANCE...BUT NOT AS AGGRESSIVE AS
THE GFDL/HWRF. THE UPDATED FORECAST IS SLIGHTLY BELOW THE PREVIOUS
ADVISORY.
 
IRENE HAS BEEN MOVING WEST-NORTHWESTWARD OR 295 DEGREES AT 10 KT. A
MID/UPPER-LEVEL TROUGH MOVING OVER THE NORTHEASTERN UNITED STATES
IS EXPECTED TO WEAKEN THE WESTERN PORTION OF THE SUBTROPICAL RIDGE
DURING THE NEXT DAY OR SO. THIS SHOULD ALLOW IRENE TO TURN
NORTHWESTWARD WITHIN THE NEXT 24-36 HOURS...AND THE TRACK GUIDANCE
IS IN EXCELLENT AGREEMENT DURING THE FIRST 48 HOURS. LATER IN THE
FORECAST PERIOD IRENE IS FORECAST TO TURN NORTHWARD AS IT ROUNDS
THE WESTERN PORTION OF THE RIDGE. THE SPREAD IN THE GUIDANCE
INCREASES BY DAY THREE...RANGING FROM THE COASTAL MID-ATLANTIC
STATES TO WELL OFFSHORE...WITH THE UKMET ALONG THE LEFT SIDE AND
THE GFS/NOGAPS ALONG THE RIGHT SIDE OF THE GUIDANCE ENVELOPE. THE
UPDATED TRACK IS CLOSEST TO THE ECMWF AND IS A LITTLE LEFT OF THE
MULTI-MODEL CONSENSUS. IT IS IMPORTANT TO REMIND USERS NOT TO FOCUS
ON THE EXACT FORECAST TRACK...ESPECIALLY AT DAYS 4 AND 5...SINCE
THE MOST RECENT 5-YEAR AVERAGE ERRORS AT THOSE FORECAST TIMES ARE
200 AND 250 MILES...RESPECTIVELY.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/1500Z 20.5N  71.0W   85 KT 100 MPH
 12H  24/0000Z 21.3N  72.3W   90 KT 105 MPH
 24H  24/1200Z 22.3N  73.8W  100 KT 115 MPH
 36H  25/0000Z 23.6N  75.2W  105 KT 120 MPH
 48H  25/1200Z 25.3N  76.5W  110 KT 125 MPH
 72H  26/1200Z 29.2N  77.5W  110 KT 125 MPH
 96H  27/1200Z 33.0N  77.5W  100 KT 115 MPH
120H  28/1200Z 37.5N  76.0W   65 KT  75 MPH...INLAND
 
$$
FORECASTER BROWN
 

WTNT44 KNHC 232053
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  14
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 PM EDT TUE AUG 23 2011
 
THE EYE OF IRENE WAS MORE APPARENT IN VISIBLE SATELLITE IMAGERY
EARLY THIS AFTERNOON...BUT HAS RECENTLY BECOME OBSCURED.  THE AIR
FORCE RESERVE HURRICANE HUNTER AIRCRAFT FOUND A MAXIMUM 700 MB
FLIGHT-LEVEL WIND OF 74 KT AND PEAK SFMR WINDS OF AROUND 75 KT. IT
HAS BEEN NEARLY 24 HOURS SINCE THE AIRCRAFT HAS MEASURED WINDS THAT
SUPPORT AN INTENSITY OF 85 KT.  THEREFORE...THE INITIAL INTENSITY
HAS BEEN REDUCED TO 80 KT.  THE PRESSURE DROPPED ABOUT A MILLIBAR
ON EACH SUCCESSIVE FIX AND WAS DOWN TO 976 MB ON THE LASS PASS
AROUND 1830 UTC.  ANOTHER HURRICANE HUNTER AIRCRAFT WILL
INVESTIGATE IRENE THIS EVENING.
 
THE HURRICANE WILL BE TRAVERSING VERY WARM WATERS DURING THE NEXT
COUPLE OF DAYS. HOWEVER...THE UPPER-LEVEL PATTERN IS NOT IDEAL FOR
RAPID DEVELOPMENT...AND THE GLOBAL MODELS SUGGEST MODERATE WESTERLY
SHEAR WILL CONTINUE FOR ANOTHER DAY OR TWO. THE NEW INTENSITY
FORECAST IS SLIGHTLY BELOW THE PREVIOUS ADVISORY DURING THE FIRST
24 HOURS DUE TO THE LOWER INITIAL INTENSITY. AFTER THAT...IT IS
UNCHANGED FROM THE PREVIOUS FORECAST AND BRINGS IRENE TO MAJOR
HURRICANE STATUS IN 36 HOURS. THE NEW INTENSITY FORECAST IS A BLEND
OF THE LOWER STATISTICAL GUIDANCE AND THE MORE AGGRESSIVE GFDL/HWRF
MODELS. 
 
THE AIRCRAFT FIXES INDICATE THAT IRENE HAS BEEN MOVING
WEST-NORTHWEST OR 295/8 KT...A LITTLE SLOWER THAN BEFORE. THE TRACK
FORECAST REASONING REMAINS UNCHANGED. IRENE IS EXPECTED TO TURN
NORTHWESTWARD THEN NORTHWARD DURING THE NEXT 2-3 DAYS AS THE
WESTERN PORTION OF THE SUBTROPICAL RIDGE WEAKENS. THE TRACK
GUIDANCE IS IN REMARKABLY GOOD AGREEMENT DURING THIS TIME AND THERE
IS HIGH CONFIDENCE IN THAT PORTION OF THE FORECAST. AFTER THAT...
IRENE IS FORECAST TO MOVE NORTHWARD TO NORTHEASTWARD AROUND THE
ATLANTIC RIDGE. SEVERAL OF THE MODELS...INCLUDING THE
GFS...ECMWF...HWRF...AND GFDL...SHOW A TURN BACK TOWARD THE NORTH
NEAR THE END OF THE FORECAST PERIOD. THIS APPEARS TO BE IN RESPONSE
TO A WEAK TROUGH THAT MOVES THROUGH THE SOUTHEASTERN UNITED STATES
BEHIND THE HURRICANE. THE UPDATED TRACK FORECAST HAS BEEN SHIFTED
EASTWARD AT 72 AND 96 HOURS BUT THE NEW 5-DAY POINT IS STILL ALONG
THE LEFT SIDE OF THE GUIDANCE ENVELOPE...IN AGREEMENT WITH THE
MODELS MENTIONED ABOVE. USERS ARE REMINDED THAT LARGE FORECAST
ERRORS ARE POSSIBLE AT THE LONGER LEAD TIMES.  

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/2100Z 20.9N  71.5W   80 KT  90 MPH
 12H  24/0600Z 21.5N  72.7W   85 KT 100 MPH
 24H  24/1800Z 22.7N  74.2W   95 KT 110 MPH
 36H  25/0600Z 24.2N  75.5W  105 KT 120 MPH
 48H  25/1800Z 26.1N  76.7W  110 KT 125 MPH
 72H  26/1800Z 30.0N  77.2W  110 KT 125 MPH
 96H  27/1800Z 34.0N  76.2W  100 KT 115 MPH
120H  28/1800Z 39.0N  74.8W   75 KT  85 MPH
 
$$
FORECASTER BROWN
 

WTNT44 KNHC 240259
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  15
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 PM EDT TUE AUG 23 2011
 
IT IS FORTUNATE THAT WE HAVE A NOAA HIGH ALTITUDE JET SAMPLING THE
ENVIRONMENT OF IRENE AND TWO HURRICANE HUNTER AIRCRAFT...ONE FROM
NOAA AND THE OTHER FROM THE AIR FORCE...IN THE EYE OF THE HURRICANE
TONIGHT. THE SATELLITE PRESENTATION HAS IMPROVED WITH A RAGGED EYE
EMBEDDED IN DEEP CONVECTION AND A WELL ESTABLISHED OUTFLOW.  THIS
HAS RESULTED IN THE INCREASE OF BOTH OBJECTIVE AND SUBJECTIVE
T-NUMBERS. THE CENTRAL PRESSURE REPORTED FROM BOTH PLANES HAS COME
DOWN TO 969 MB AND THE MAX FLIGHT-LEVEL WIND MEASURED WAS 101
KNOTS. HOWEVER...DATA FROM THE SFMR INDICATE THAT THE SURFACE WINDS
HAVE NOT INCREASED YET AND THE INITIAL INTENSITY REMAINS AT 80
KNOTS.  IRENE WILL BE TRAVERSING VERY WARM WATERS AND ALTHOUGH THE
UPPER-LEVEL WINDS ARE NOT IDEAL FOR RAPID INTENSIFICATION...THE
OVERALL CONDITIONS FAVOR STRENGTHENING DURING THE NEXT DAY OR TWO
AS INDICATED IN THE PREVIOUS FORECAST...AND IRENE IS EXPECTED TO BE
A MAJOR HURRICANE AS IT MOVES OVER THE CENTRAL BAHAMAS IN ABOUT A
DAY. 

SATELLITE AND RECONNAISSANCE FIXES INDICATE THAT IRENE IS STILL
MOVING TOWARD THE WEST-NORTHWEST AT A SLOW PACE OF 8 KNOTS. SINCE
THERE HAS BEEN NO CHANGE IN THE EXPECTED EVOLUTION OF THE STEERING
PATTERN...THERE IS NO REASON TO MODIFY THE PREVIOUS OFFICIAL
FORECAST WHICH BRINGS THE HURRICANE NORTHWESTWARD ACROSS THE
BAHAMAS...AND THEN NORTHWARD PARALLELING THE UNITED STATES
SOUTHEAST COAST AND VERY CLOSE TO OR OVER THE OUTER BANKS. IRENE
SHOULD CONTINUE NORTHWARD OR NORTH-NORTHEASTWARD ALONG THE MID
ATLANTIC COAST. THE TRACK GUIDANCE IS IN BETTER AGREEMENT TONIGHT
AND EVEN THE STUBBORN GFDL WHICH PREVIOUSLY INSISTED ON BRINGING
IRENE TOWARD FLORIDA HAS NOW SHIFTED EASTWARD AND HAS JOINED THE
OTHER DYNAMICAL MODELS. THIS INCREASES THE CONFIDENCE IN THE TRACK
FORECAST EVEN MORE.

USERS ARE REMINDED THAT LARGE FORECAST ERRORS ARE POSSIBLE AT THE
LONGER LEAD TIMES.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/0300Z 21.3N  72.4W   80 KT  90 MPH
 12H  24/1200Z 22.0N  73.5W   85 KT 100 MPH
 24H  25/0000Z 23.5N  75.0W   95 KT 110 MPH
 36H  25/1200Z 25.5N  76.5W  105 KT 120 MPH
 48H  26/0000Z 27.5N  77.0W  110 KT 125 MPH
 72H  27/0000Z 31.0N  77.0W  110 KT 125 MPH
 96H  28/0000Z 36.0N  76.0W  100 KT 115 MPH
120H  29/0000Z 40.5N  73.5W   75 KT  85 MPH
 
$$
FORECASTER AVILA
 

WTNT44 KNHC 240846
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  16
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 AM EDT WED AUG 24 2011
 
THE LAST PENETRATION OF THE EYE BY THE AIR FORCE HURRICANE HUNTERS
WAS JUST AFTER 0500 UTC...AND THEY FOUND THAT THE CENTRAL PRESSURE
HAD DROPPED TO 966 MB.  THEY ALSO MEASURED 700 MB FLIGHT-LEVEL WINDS
OF 92 KT OUTBOUND IN THE SOUTHEAST QUADRANT.  IT IS LIKELY THAT
HIGHER WINDS WERE OCCURRING OVER THE NORTHEAST QUADRANT OF THE
HURRICANE.  OVER THE PAST FEW HOURS..THE SATELLITE PRESENTATION OF
IRENE HAS BECOME QUITE IMPRESSIVE WITH THE EYE EMBEDDED WITHIN VERY
COLD CLOUD TOPS.  DVORAK INTENSITY ESTIMATES FROM BOTH TAFB AND SAB
ARE 100 KT.  COMBINING THE ABOVE INFORMATION...THE CURRENT
INTENSITY IS SET CONSERVATIVELY AT 95 KT FOR THIS ADVISORY.  ANOTHER
HURRICANE HUNTER MISSION IS SCHEDULED FOR 1200 UTC TO MEASURE THE
INTENSITY OF THE HURRICANE.  ALTHOUGH THE NUMERICAL GUIDANCE
INDICATES SOME SOUTH-SOUTHWESTERLY SHEAR OVER THE AREA...THIS SHEAR
IS NOT EXPECTED TO PREVENT FURTHER STRENGTHENING AND IT SEEMS
HIGHLY LIKELY THAT IRENE WILL INTENSIFY TO CATEGORY 3 STATUS LATER
TODAY.  SOME FLUCTUATIONS IN STRENGTH COULD OCCUR IN 1 TO 2 DAYS
DUE TO EYEWALL REPLACEMENTS.  IN FACT...THE UW-CIMSS OBJECTIVE
TECHNIQUE SHOWS A CONSIDERABLY HIGHER THAN CLIMATOLOGICAL
PROBABILITY OF SECONDARY EYEWALL FORMATION WITHIN 24 TO 48 HOURS. 
THE OFFICIAL INTENSITY FORECAST IS CLOSE TO THE NUMERICAL CONSENSUS
AND LIES BETWEEN THE GFDL/HWRF MODELS AND THE LGEM GUIDANCE.
 
SATELLITE ANIMATION AND CENTER FIXES SHOW THAT THE EYE OF IRENE HAS
BEEN WOBBLING BETWEEN A WEST AND NORTHWEST HEADING OVER THE PAST
SEVERAL HOURS.  SMOOTHING THROUGH THESE WOBBLES YIELDS A MORE
REPRESENTATIVE MOTION OF ABOUT 295/8.  THERE HAS BEEN LITTLE CHANGE
TO THE TRACK FORECAST REASONING FROM THE PAST FEW ADVISORIES.  OVER
THE NEXT COUPLE OF DAYS...THE HURRICANE IS EXPECTED TO GRADUALLY
TURN TOWARD THE NORTHWEST AND NORTH AS IT MOVES THROUGH A
PRONOUNCED WEAKNESS IN THE SUBTROPICAL RIDGE.  AROUND 72 HOURS...A
SHORTWAVE TROUGH MOVING THROUGH THE GREAT LAKES SHOULD BEGIN TO
INDUCE AT LEAST A SLIGHT TURN TOWARD THE NORTH-NORTHEAST WITH SOME
ACCELERATION AFTERWARDS.  THE DYNAMICAL TRACK MODEL CONSENSUS
HAS...AGAIN...SHIFTED A LITTLE TO THE EAST FROM THE PREVIOUS
PACKAGE.  THE OFFICIAL FORECAST IS NOT SUBSTANTIALLY DIFFERENT FROM
THE PREVIOUS ONE AND LIES A LITTLE TO THE LEFT OF THE CONSENSUS.
 
USERS ARE REMINDED THAT SIGNIFICANT ERRORS ARE POSSIBLE WITH
FORECASTS AT LONGER LEAD TIMES...SO ONE SHOULD NOT FOCUS ON THE
EXACT FORECAST POSITIONS AT 96 AND 120 HOURS.
 
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/0900Z 21.6N  72.9W   95 KT 110 MPH
 12H  24/1800Z 22.5N  74.1W  105 KT 120 MPH
 24H  25/0600Z 24.1N  75.4W  110 KT 125 MPH
 36H  25/1800Z 25.8N  76.6W  110 KT 125 MPH
 48H  26/0600Z 27.7N  77.0W  110 KT 125 MPH
 72H  27/0600Z 32.0N  76.8W  105 KT 120 MPH
 96H  28/0600Z 36.5N  75.0W   90 KT 105 MPH
120H  29/0600Z 42.0N  71.5W   70 KT  80 MPH...INLAND
 
$$
FORECASTER PASCH/KIMBERLAIN
 

WTNT44 KNHC 241450
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  17
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 AM EDT WED AUG 24 2011
 
IRENE HAS CONTINUED TO STRENGTHEN THIS MORNING.  THE EYE HAS BECOME
MORE DISTINCT IN SATELLITE IMAGERY AND IT IS SURROUNDED BY CLOUD
TOPS COLDER THAN -70 DEGREES CELSIUS.  BOTH AIR FORCE AND NOAA
HURRICANE HUNTER AIRCRAFT HAVE BEEN INVESTIGATING IRENE THIS
MORNING.  THE AIR FORCE PLANE MEASURED A PEAK 700 MB FLIGHT-LEVEL
WIND OF 112 KT JUST BEFORE 1200 UTC...AND THIS SUPPORTED THE
UPGRADE TO A 100-KT CATEGORY THREE HURRICANE AT THAT TIME.  SINCE
THAT TIME THE NOAA AIRCRAFT REPORTED 115 KT AT 750 MB.  THE
PRESSURE HAS REMAINED AROUND 956 MB...AND THE INITIAL INTENSITY
ESTIMATE REMAINS 100 KT.
 
THE OUTFLOW HAS BECOME WELL ESTABLISHED OVER THE HURRICANE AND IRENE
WILL BE MOVING OVER SEA SURFACE TEMPERATURES OF AROUND 29 DEGREES
CELSIUS DURING THE NEXT 24-36 HOURS.  THESE ENVIRONMENTAL FACTORS
FAVOR ADDITIONAL INTENSIFICATION AND THE NEW INTENSITY FORECAST
CALLS FOR IRENE TO REACH CATEGORY FOUR STRENGTH WITHIN 24 HOURS. 
AFTER THAT TIME...SOME FLUCTUATIONS IN WIND SPEEDS ARE LIKELY DUE
TO EYEWALL REPLACEMENTS.  THE UW-CIMSS OBJECTIVE SECONDARY EYEWALL
FORMATION TECHNIQUE SHOWS A VERY HIGH LIKELIHOOD OF THAT OCCURRING
DURING THE NEXT 48 HOURS.  SOUTHWESTERLY SHEAR IS EXPECTED TO
GRADUALLY INCREASE AND THE HURRICANE WILL BE MOVING OVER
SIGNIFICANTLY COLDER WATERS BY 96 HOURS.  THIS SHOULD RESULT IN
GRADUAL WEAKENING...HOWEVER IRENE IS FORECAST TO REMAIN A LARGE AND
POWERFUL HURRICANE DURING THE NEXT 5 DAYS.
 
AIRCRAFT FIXES DURING THE PAST 12 HOURS INDICATE THAT IRENE HAS MADE
THE EXPECTED TURN TOWARD THE NORTHWEST...WITH AN INITIAL MOTION OF
305/10. THERE IS NO CHANGE TO THE TRACK FORECAST REASONING AND THE
MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT FOR THE FIRST 2-3
DAYS. AFTER THAT TIME...THERE IS SOME QUESTION AS TO WHETHER OR NOT
IRENE CONTINUES ON A NORTH-NORTHEAST HEADING OR TURNS BACK TOWARD
THE NORTH AHEAD OF A MID-LATITUDE TROUGH APPROACHING THE GREAT
LAKES REGION. THE GFDL AND HWRF MODELS REMAIN ALONG THE WEST SIDE
OF THE GUIDANCE ENVELOPE AND SHOW A TRACK OVER OR VERY CLOSE TO THE
MID-ATLANTIC COAST. THE UKMET AND NOGAPS ARE ALONG THE EASTERN SIDE
AND KEEP THE CORE OF THE HURRICANE WELL OFFSHORE. GIVEN THE TYPICAL
MODEL AND OFFICIAL TRACK ERRORS...BOTH SCENARIOS ARE VIABLE OPTIONS
AT THIS TIME...AND USERS ARE ONCE AGAIN REMINDED NOT TO FOCUS ON
SPECIFIC FORECAST POINTS THREE TO FIVE DAYS DOWNSTREAM. THE TVCA
CONSENSUS AND THE EXPERIMENTAL HURRICANE FORECAST IMPROVEMENT
PROJECT CONSENSUS WERE RELATIVELY CLOSE TO THE PREVIOUS NHC
FORECAST. THE UPDATED NHC TRACK HAS BEEN NUDGED EASTWARD AT 96 AND
120 HOURS AND LIES BETWEEN THOSE TWO CONSENSUS AIDS.
 
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/1500Z 22.4N  73.9W  100 KT 115 MPH
 12H  25/0000Z 23.4N  74.8W  110 KT 125 MPH
 24H  25/1200Z 25.1N  76.1W  115 KT 135 MPH
 36H  26/0000Z 27.2N  76.9W  115 KT 135 MPH
 48H  26/1200Z 29.3N  77.2W  110 KT 125 MPH
 72H  27/1200Z 33.2N  76.2W  100 KT 115 MPH
 96H  28/1200Z 38.5N  73.5W   85 KT 100 MPH
120H  29/1200Z 45.0N  69.5W   70 KT  80 MPH...INLAND
 
$$
FORECASTER BROWN
 

WTNT44 KNHC 242053
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 PM EDT WED AUG 24 2011
 
THE SATELLITE PRESENTATION OF THE HURRICANE HAS CONTINUED TO IMPROVE
THIS AFTERNOON.  A LARGE AREA OF DEEP CONVECTION WITH VERY COLD
CLOUD TOPS HAS EXPANDED NEAR THE EYEWALL AND NOW SOLIDLY SURROUNDS
THE EYE.  BEFORE DEPARTING IRENE...THE AIR FORCE RESERVE HURRICANE
HUNTER AIRCRAFT MEASURED A PEAK 700 MB FLIGHT-LEVEL WIND OF 116 KT
IN THE NORTHEASTERN EYEWALL AND A DROPSONDE MEASURED A MINIMUM
PRESSURE OF 954 MB.  THESE DATA SUPPORT AN INITIAL INTENSITY OF
105 KT.
 
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE FOR SOME
ADDITIONAL STRENGTHENING DURING THE NEXT DAY OR TWO. THE UW-CIMMS
OBJECTIVE SECONDARY EYEWALL FORMATION TECHNIQUE CONTINUES TO
PREDICT A HIGH CHANCE OF AN EYEWALL REPLACEMENT DURING THE NEXT DAY
OR SO. IN FACT...A RECENT TRMM MICROWAVE PASS SHOWED SOME EVIDENCE
OF A SECONDARY EYEWALL. THESE EYEWALL CYCLES CAN PRODUCE HARD TO
PREDICT FLUCTUATIONS IN INTENSITY. FOR NOW...THE NEW INTENSITY
FORECAST CALL FOR SOME ADDITIONAL STRENGTHENING FOLLOWED BY A
LEVELING OFF OF THE INTENSITY. IN 3-4 DAYS....INCREASING
SOUTHWESTERLY SHEAR AND COOLER SSTS SHOULD INDUCE GRADUAL
WEAKENING...ALTHOUGH IRENE IS EXPECTED TO REMAIN A LARGE AND
POWERFUL HURRICANE...OR EVEN GROW IN SIZE...AS IT NEARS NEW
ENGLAND. 
 
THE HURRICANE HAS BEEN MOVING NORTHWESTWARD OR 310/10 KT. IRENE IS
EXPECTED TO TURN TOWARD THE NORTH-NORTHWEST THEN NORTH THROUGH A
BREAK IN THE SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC DURING
THE NEXT COUPLE OF DAYS.  AFTER THAT TIME...THE HURRICANE IS
FORECAST TO TURN NORTH-NORTHEASTWARD AROUND THE NORTHWESTERN SIDE
OF THE RIDGE.  BETWEEN 72 AND 96 HOURS...THERE REMAINS UNCERTAINTY
AS TO WHETHER IRENE TURNS BACK TOWARD THE NORTH AHEAD OF A
MID-LATITUDE TROUGH MOVING INTO THE GREAT LAKES REGION AT THAT
TIME.  THE NEW ECMWF SHOWS MUCH MORE AMPLIFICATION OF THE TROUGH...
WHICH HAS RESULTED IN ITS TRACK SHIFTING OVER 100 MILES TO THE
WEST...AND THIS SKILLFUL LONG-RANGE MODEL NOW DEFINES THE WESTERN
EDGE OF THE GUIDANCE ENVELOPE.  OVERALL...THE GUIDANCE ENVELOPE HAS
SHIFTED A LITTLE WESTWARD AT DAYS 4 AND 5. THE NEW TRACK FORECAST
IS CLOSE TO THE PREVIOUS ADVISORY AND IS BETWEEN THE GFS
AND ECMWF MODELS.  THIS IS ALSO CLOSE TO THE TVCA AND EXPERIMENTAL
HURRICANE FORECAST IMPROVEMENT PROJECT...HFIP...CONSENSUS TRACKS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/2100Z 23.1N  74.7W  105 KT 120 MPH
 12H  25/0600Z 24.3N  75.8W  110 KT 125 MPH
 24H  25/1800Z 26.1N  76.8W  115 KT 135 MPH
 36H  26/0600Z 28.2N  77.3W  115 KT 135 MPH
 48H  26/1800Z 30.1N  77.3W  110 KT 125 MPH
 72H  27/1800Z 34.3N  75.8W  100 KT 115 MPH
 96H  28/1800Z 39.5N  73.0W   85 KT 100 MPH
120H  29/1800Z 47.0N  69.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BROWN
 

WTNT44 KNHC 250256
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  19
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 PM EDT WED AUG 24 2011
 
AN AIR FORCE RECONNAISSANCE PLANE ESTIMATED A MINIMUM PRESSURE OF
952 MB...BUT THE MAXIMUM WIND REPORTED SO FAR WAS 99 KNOTS AT
FLIGHT LEVEL. THE OVERALL CLOUD PATTERN HAS NOT CHANGED
SIGNIFICANTLY DURING THE PAST FEW HOURS AND SATELLITE INTENSITY
ESTIMATES STILL SUPPORT 105 KNOTS. I WILL WAIT FOR THE PLANE TO
FINISH SAMPLING THE HURRICANE BEFORE REDUCING THE WINDS A LITTLE
BIT...IF NECESSARY. BY INSPECTING AN EARLIER TRMM PASS FROM 2216
UTC...AND AND SSMIS AT 0024 UTC...ONE CAN OBSERVE CONCENTRIC
CONVECTIVE RINGS SUGGESTING THAT AN EYEWALL REPLACEMENT CYCLE IS
OCCURRING. THESE TWO EYEWALLS WERE ALSO REPORTED BY THE AIR FORCE
RECONNAISSANCE PLANE. THIS EYEWALL CYCLE WILL LIKELY RESULT IN SOME
FLUCTUATIONS IN INTENSITY DURING THE NEXT FEW HOURS...BUT THE TREND
IS FOR IRENE TO INTENSIFY A LITTLE MORE DURING THE NEXT 24 HOURS.
IN 2 TO 3 DAYS....IRENE SHOULD BEGIN TO GRADUALLY WEAKEN AS THE
HURRICANE ENCOUNTERS INCREASING SOUTHWESTERLY SHEAR AND COOLER
SSTS. IRENE IS EXPECTED TO REMAIN A LARGE AND POWERFUL HURRICANE...
OR EVEN GROW IN SIZE...AS IT MOVES NEAR THE NORTHEASTERN UNITED
STATES.
 
THE EYE OF THE HURRICANE HAS BEEN MOVING NEAR OR OVER SOME OF THE
BAHAMAS RESULTING IS SOME WOBBLING. THE BEST ESTIMATE OF THE
INITIAL MOTION IS TOWARD THE NORTHWEST OR 310 DEGREES AT 10 KNOTS.
THE DEVELOPMENT OF THE LARGE TROUGH ALONG THE EAST COAST OF THE
UNITED STATES IS MATERIALIZING AS PREDICTED BY THE GLOBAL MODELS. 
THIS STEERING PATTERN WILL FORCE IRENE TO TURN TOWARD THE
NORTH-NORTHWEST AND THE NORTH WITH A SLIGHT INCREASE IN FORWARD
SPEED OVER THE NEXT FEW DAYS. THE LATEST GUIDANCE HAS CHANGED VERY
LITTLE...AND PERHAPS THE ONLY DIFFERENCE IS THAT THE GFS SHIFTED 30
N MI TO THE WEST...TOWARD THE ECMWF SOLUTION DURING THE LAST
PORTION OF THE FORECAST. THIS DOES NOT RESULT IN A SIGNIFICANT
CHANGE OF THE OFFICIAL FORECAST TRACK FROM THE PREVIOUS ONE.
 
BECAUSE IRENE IS A LARGE CYCLONE...TROPICAL STORM AND HURRICANE
WATCHES WILL LIKELY BE REQUIRED FOR A PORTION OF THE COAST OF THE
CAROLINAS EARLY THURSDAY.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  25/0300Z 23.8N  75.4W  105 KT 120 MPH
 12H  25/1200Z 25.5N  76.5W  110 KT 125 MPH
 24H  26/0000Z 27.5N  77.3W  115 KT 135 MPH
 36H  26/1200Z 29.5N  77.4W  110 KT 125 MPH
 48H  27/0000Z 31.5N  77.0W  105 KT 120 MPH
 72H  28/0000Z 36.0N  75.2W   90 KT 105 MPH
 96H  29/0000Z 42.5N  72.0W   75 KT  85 MPH
120H  30/0000Z 50.0N  67.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER AVILA
 

WTNT44 KNHC 250858
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 AM EDT THU AUG 25 2011
 
A HURRICANE HUNTER AIRCRAFT INVESTIGATING IRENE A FEW HOURS AGO
FOUND THAT THE CENTRAL PRESSURE HAD DROPPED TO 950 MB. 
HOWEVER...FLIGHT-LEVEL AND SFMR-OBSERVED SURFACE WIND DATA
SUPPORTED A CURRENT INTENSITY OF NO MORE THAN 100 KT...AND THIS IS
PROBABLY GENEROUS.  IT IS PRESUMED THAT THE INTENSIFICATION PROCESS
WAS HALTED BY AN EYEWALL REPLACEMENT EVENT AS SUGGESTED BY
MICROWAVE IMAGERY AND AIRCRAFT OBSERVATIONS.  SINCE THE ENVIRONMENT
APPEARS TO BE CONDUCIVE WITH WEAK SHEAR...WARM WATERS...AND AN
UPPER-LEVEL OUTFLOW ANTICYCLONE OVER THE HURRICANE...THE OFFICIAL
FORECAST SHOWS RE-STRENGTHENING WITHIN A DAY OR SO.  AFTER A COUPLE
OF DAYS...THE SHIPS GUIDANCE SHOWS A SIGNIFICANT INCREASE IN
VERTICAL SHEAR...SO A STEADY DECREASE IN INTENSITY IS LIKELY. 
HOWEVER...SINCE IRENE HAS SUCH A LARGE AND INTENSE CIRCULATION...IT
WILL PROBABLY BE RATHER SLOW TO WEAKEN.  GIVEN THE LIMITATIONS IN
OUR ABILITY TO PREDICT INTENSITY CHANGE...THERE IS SIGNIFICANT
UNCERTAINTY AS TO JUST HOW STRONG IRENE WILL BE WHEN IT NEARS THE
EASTERN AND NORTHEASTERN U.S. COAST.

THE INITIAL MOTION CONTINUES TO BE ABOUT 315/10.  THERE HAS BEEN NO
CHANGE TO THE TRACK FORECAST REASONING.  IRENE SHOULD TURN
NORTHWARD AS IT MOVES THROUGH A BREAK IN THE SUBTROPICAL RIDGE
DURING THE NEXT 48 HOURS.  THEREAFTER...A SHORTWAVE TROUGH MOVING
THROUGH THE GREAT LAKES IS LIKELY TO TURN THE HURRICANE TOWARD THE
NORTH-NORTHEAST.  IN THE LATTER PART OF THE FORECAST
PERIOD...GLOBAL MODELS SHOW THE SHORTWAVE BYPASSING IRENE AND THE
HURRICANE BECOMING EMBEDDED WITHIN A BROAD AND SLOW-MOVING
MID-TROPOSPHERIC TROUGH OVER THE EASTERN UNITED STATES.  THIS
STEERING PATTERN SHOULD PREVENT IRENE FROM MOVING WELL OFFSHORE OF
THE NORTHEASTERN STATES.  THE OFFICIAL TRACK FORECAST HAS BEEN
SHIFTED VERY SLIGHTLY TO THE WEST OF THE PREVIOUS ONE AND IS
ROUGHLY IN THE MIDDLE OF THE GUIDANCE ENVELOPE...WHICH IS BRACKETED
BY THE U.K. MET. OFFICE MODEL ON THE EAST AND THE GFDL MODEL ON THE
WEST.

HURRICANE AND TROPICAL STORM WATCHES ARE NOW NECESSARY FOR A PORTION
OF THE SOUTHEAST AND CENTRAL U.S. EAST COAST. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  25/0900Z 24.6N  76.2W  100 KT 115 MPH
 12H  25/1800Z 26.1N  77.1W  110 KT 125 MPH
 24H  26/0600Z 28.2N  77.7W  115 KT 135 MPH
 36H  26/1800Z 30.4N  77.5W  110 KT 125 MPH
 48H  27/0600Z 32.3N  77.1W  100 KT 115 MPH
 72H  28/0600Z 36.3N  75.4W   90 KT 105 MPH
 96H  29/0600Z 42.5N  72.5W   60 KT  70 MPH...INLAND
120H  30/0600Z 51.0N  67.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER PASCH
 

WTNT44 KNHC 251455
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  21
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 AM EDT THU AUG 25 2011

IT HAS BEEN DIFFICULT TO DETERMINE WHETHER THE HURRICANE HAS GONE
THROUGH AN EYEWALL REPLACEMENT. ALTHOUGH THE RADIUS OF MAXIMUM WIND
IS LARGER TODAY THAN YESTERDAY...MICROWAVE AND AIRCRAFT DATA HAVE
NOT BEEN VERY CONCLUSIVE. RECENT DATA DO NOT SHOW ANY EVIDENCE OF A
SECONDARY EYEWALL AT THIS TIME. THE EYE IS A LITTLE MORE EVIDENT IN
THE LAST FEW VISIBLE SATELLITE IMAGES...BUT IS NOT AS CLEAR AS IT
WAS YESTERDAY MORNING. THE AIR FORCE AIRCRAFT HAS MEASURED A PEAK
FLIGHT-LEVEL WIND OF 112 KT AND SFMR WINDS OF 90 KT...WHICH ROUGHLY
SUPPORT THE 100-KT INITIAL INTENSITY.
 
CENTER FIXES FROM THE AIRCRAFT OVERNIGHT AND THIS MORNING INDICATE
THAT THE EXPECTED NORTH-NORTHWESTWARD TURN HAS OCCURRED. A
NORTHWARD TURN IS EXPECTED TONIGHT OR EARLY FRIDAY AS IRENE MOVES
THROUGH A BREAK IN THE SUBTROPICAL RIDGE. A MID/UPPER-LEVEL TROUGH
MOVING THROUGH THE GREAT LAKES REGION IS EXPECTED TO THEN TURN
IRENE TOWARD THE NORTH-NORTHEAST IN A COUPLE OF DAYS. THIS TROUGH
IS FORECAST TO BYPASS IRENE...LEAVING THE HURRICANE IN DEEP
SOUTHERLY FLOW BETWEEN A TROUGH OVER THE CENTRAL UNITED STATES AND
A BUILDING RIDGE OVER THE ATLANTIC. THIS PATTERN WILL LIKELY KEEP
THE HURRICANE VERY NEAR THE EAST COAST OF THE UNITED STATES. THE
GUIDANCE ENVELOPE HAS SHIFTED A LITTLE WESTWARD ON THIS CYCLE...AND
THE NEW OFFICIAL TRACK HAS BEEN NUDGED WEST AS WELL. THE NEW
FORECAST LIES BETWEEN THE GFS AND ECMWF...AND IS A LITTLE RIGHT OF
THE TVCA CONSENSUS. SINCE IRENE IS SUCH A LARGE TROPICAL
CYCLONE...SIGNIFICANT IMPACTS ARE LIKELY ALONG THE UNITED STATES
EAST COAST REGARDLESS OF THE EXACT TRACK IT TAKES.

THE ENVIRONMENT REMAINS CONDUCIVE FOR SOME ADDITIONAL STRENGTHENING
DURING THE NEXT DAY OR TWO.  THE MAIN INFLUENCING FACTOR DURING THE
SHORT TERM WILL LIKELY BE EYEWALL CYCLES WHICH ARE DIFFICULT TO
PREDICT.  AFTER 48 HOURS...SOUTHWESTERLY SHEAR IS FORECAST TO
INCREASE WHICH WILL LIKELY START WEAKENING PROCESS.  HOWEVER...
SINCE IRENE HAS SUCH A LARGE AND INTENSE CIRCULATION...IT
WILL PROBABLY BE RATHER SLOW TO WEAKEN.   
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  25/1500Z 25.9N  76.8W  100 KT 115 MPH
 12H  26/0000Z 27.5N  77.5W  105 KT 120 MPH
 24H  26/1200Z 29.5N  77.8W  110 KT 125 MPH
 36H  27/0000Z 31.4N  77.5W  105 KT 120 MPH
 48H  27/1200Z 33.3N  77.1W  100 KT 115 MPH
 72H  28/1200Z 37.8N  75.3W   85 KT 100 MPH
 96H  29/1200Z 45.0N  71.5W   55 KT  65 MPH...INLAND
120H  30/1200Z 54.0N  64.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BROWN
 

WTNT44 KNHC 252052
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  22
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 PM EDT THU AUG 25 2011
 
THE EYE OF IRENE MOVED OVER ABACO ISLAND EARLIER THIS AFTERNOON. AN
AUTOMATED WEATHER STATION ON THE ISLAND MEASURED A MINIMUM PRESSURE
OF 950.4 MB AROUND 1700 UTC. THE AIR FORCE RESERVE HURRICANE HUNTER
AIRCRAFT INVESTIGATING IRENE THIS AFTERNOON HAS REPORTED A 700 MB
PEAK-FLIGHT WIND OF 99 KT. ALTHOUGH RECENT AIRCRAFT DATA DO NOT
QUITE SUPPORT THE 100-KT ADVISORY INTENSITY...WE WILL HOLD THE
INTENSITY FOR A LITTLE LONGER TO SEE IF THE AIRCRAFT FINDS HIGHER
WINDS.

IRENE CONTINUES MOVING NORTH-NORTHWESTWARD AT ABOUT 12 KT. THERE HAS
BEEN NO CHANGE TO THE TRACK FORECAST REASONING. IRENE IS FORECAST
TO TURN NORTHWARD BY EARLY FRIDAY AS IT MOVES THROUGH A BREAK IN
THE SUBTROPICAL RIDGE. AFTER 24 HOURS...THE HURRICANE IS EXPECTED
TO MOVE ON A HEADING BETWEEN NORTH AND NORTH-NORTHEAST AS A TROUGH
BYPASSES THE CYCLONE TO THE NORTH. THIS WILL LEAVE THE IRENE IN A
STEERING PATTERN THAT SHOULD KEEP THE HURRICANE ON THAT GENERAL
HEADING AS IT MOVES VERY NEAR OR OVER MID-ATLANTIC COAST. THE TRACK
GUIDANCE HAS COME INTO BETTER AGREEMENT ON THIS SOLUTION...AND THE
CONFIDENCE IN THE TRACK FORECAST IS INCREASING. THE NEW TRACK HAS
BEEN NUDGED WESTWARD AND IS CLOSE TO THE CENTER OF THE GUIDANCE
ENVELOPE. IT IS ALSO IN GOOD AGREEMENT WITH THE 1200 UTC GFS. SINCE
IRENE IS A LARGE TROPICAL CYCLONE...ONE SHOULD NOT FOCUS ON THE
EXACT TRACK OF IRENE...AS SIGNIFICANT IMPACTS WILL BE FELT WELL
AWAY FROM THE CENTER.
 
THERE IS STILL SOME TIME FOR IRENE TO STRENGTHEN AS IT WILL BE
MOVING OVER WARM WATER AND THE SHEAR REMAINS LOW.  HOWEVER...THE
UPDATED FORECAST CALLS FOR A LITTLE LOWER INTENSITY OVER
THE FIRST 24-36 HOURS.  IN ABOUT 48 HOURS...SOUTHWESTERLY SHEAR IS
FORECAST TO INCREASE...WHICH SHOULD START A WEAKENING PROCESS.
HOWEVER...SINCE IRENE HAS SUCH A LARGE AND INTENSE CIRCULATION...
IT WILL PROBABLY BE SLOW TO WEAKEN.   
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  25/2100Z 27.0N  77.3W  100 KT 115 MPH
 12H  26/0600Z 28.7N  77.8W  100 KT 115 MPH
 24H  26/1800Z 30.6N  77.8W  105 KT 120 MPH
 36H  27/0600Z 32.5N  77.4W  100 KT 115 MPH
 48H  27/1800Z 34.5N  76.9W   95 KT 110 MPH
 72H  28/1800Z 39.8N  74.6W   75 KT  85 MPH...INLAND
 96H  29/1800Z 48.5N  68.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  30/1800Z 56.0N  54.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BROWN
 

WTNT44 KNHC 260255
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  23
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 PM EDT THU AUG 25 2011
 
TWO HURRICANE HUNTER AIRCRAFT...ONE AIR FORCE AND ONE NOAA...ARE
AGAIN TONIGHT SUPPLYING VERY VALUABLE METEOROLOGICAL DATA TO THE
NATIONAL HURRICANE CENTER. BOTH PLANES INDICATE THAT THE CENTRAL
PRESSURE IS GRADUALLY FALLING AND IS NOW NEAR 942 MB...BUT THE
WINDS HAVE NOT INCREASED YET. THE INITIAL INTENSITY IS KEPT AT 100
KNOTS AT THIS TIME. IRENE HAS MOVED AWAY FROM THE NORTHWESTERN
BAHAMAS AND IS NOW OVER OPEN WATERS. THE EYE HAS BECOME A LITTLE
BETTER DEFINED ON SATELLITE AND MICROWAVE IMAGERY AND IT APPEARS
THAT THE EYEWALL IS CONTRACTING. GIVEN THE CURRENT STRUCTURE AND
THE WARM WATERS ALONG THE TRACK OF THE HURRICANE...SOME
STRENGTHENING IS INDICATED DURING THE NEXT 12 TO 24 HOURS. A SLOW
WEAKENING SHOULD BEGIN THEREAFTER...BUT IRENE IS EXPECTED TO
APPROACH THE COAST OF NORTH CAROLINA A POWERFUL HURRICANE. IN
FACT...THE HIGH RESOLUTION ECMWF SHOWS A VERY INTENSE CYCLONE
APPROACHING THE NORTH CAROLINA COAST.
 
SATELLITE AND RECONNAISSANCE FIXES INDICATE THAT IRENE IS MOVING
TOWARD THE NORTH OR 350 DEGREES AT 12 KNOTS. THE HURRICANE IS
ALREADY ON THE WEST SIDE OF THE SUBTROPICAL RIDGE AND IS READY TO
INTERACT WITH SOUTH-SOUTHWESTERLY FLOW AHEAD OF THE THE APPROACHING
MID-LATITUDE TROUGH. IRENE HAS NOWHERE TO GO BUT NORTHWARD WITH A
GRADUAL TURN TO THE NORTH-NORTHEAST AFTER THE CENTER CROSSES OR
PASSES NEAR THE NORTH CAROLINA COAST. THE TRACK GUIDANCE HAS BEEN
VERY CONSISTENT AND CONTINUES TO BE TIGHTLY CLUSTERED...GIVING NO
REASON TO MAKE A SIGNIFICANT CHANGE TO THE OFFICIAL FORECAST.
 
GIVEN THE CURRENT FORECAST...IT IS NOT NECESSARY TO ADJUST THE U.S.
WATCHES AND WARNINGS AT THIS TIME.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/0300Z 28.3N  77.3W  100 KT 115 MPH
 12H  26/1200Z 30.0N  77.8W  105 KT 120 MPH
 24H  27/0000Z 31.8N  77.6W  110 KT 125 MPH
 36H  27/1200Z 33.7N  77.1W  105 KT 120 MPH
 48H  28/0000Z 36.0N  76.3W   90 KT 105 MPH
 72H  29/0000Z 42.0N  73.0W   70 KT  80 MPH...INLAND
 96H  30/0000Z 51.0N  66.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  31/0000Z 58.0N  50.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER AVILA
 

WTNT44 KNHC 260900
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  24
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 AM EDT FRI AUG 26 2011

REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE
THAT THE INTENSITY OF IRENE IS NOT QUITE AT MAJOR HURRICANE STATUS.
THE MAXIMUM FLIGHT-LEVEL WINDS AT 700 MB WERE 109 KT ABOUT 75 N MI
EAST-NORTHEAST OF THE CENTER...AND THE MAXIMUM SURFACE WINDS
REPORTED FROM THE STEPPED FREQUENCY MICROWAVE RADIOMETER WERE 87
KT. BASED ON THESE DATA...THE INTENSITY ESTIMATE IS REDUCED TO 95
KT...WHICH IS ALSO BETWEEN THE SATELLITE INTENSITY ESTIMATES OF 102
KT FROM TAFB ANND 90 KT FROM SAB. THE AIRCRAFT DATA INDICATE THAT A
20 N MI WIDE EYE IS PRESENT AND THAT THE CENTRAL PRESSURE REMAINS
NEAR 942 MB.

THE INITIAL MOTION IS NOW 360/12. IRENE IS MOVING THROUGH A WEAKNESS
AT THE WESTERN END OF THE SUBTROPICAL RIDGE...AND IT SHOULD RECURVE
INTO THE WESTERLIES DURING THE FORECAST PERIOD. THE TRACK GUIDANCE
IS TIGHTLY CLUSTERED AROUND A NORTHWARD MOTION DURING THE FIRST 24
HR...FOLLOWED BY A TURN TOWARD THE NORTH-NORTHEAST. THE NEW
FORECAST TRACK CALLS FOR IRENE TO MAKE LANDFALL ALONG THE NORTH
CAROLINA OUTER BANKS IN ABOUT 36 HR...THEN PASS NEAR THE COAST OF
THE MID-ATLANTIC STATES BEFORE MAKING LANDFALL IN NEW ENGLAND IN
ROUGHLY 60 HOURS. THERE HAS BEEN NO SIGNIFICANT CHANGE IN THE TRACK
GUIDANCE SINCE THE LAST ADVISORY... AND WHILE THE FORECAST TRACK
HAS BEEN ADJUSTED SLIGHTLY TO THE EAST THIS SHOULD BE CONSIDERED A
NOISE-LEVEL CHANGE. AFTER LANDFALL... IRENE SHOULD MERGE WITH THE
CORE OF THE WESTERLIES AND TURN NORTHEASTWARD WITH ACCELERATION.

WATER VAPOR IMAGERY AND ANALSYES FROM CIMSS AT THE UNIVERSITY OF
WISCONSIN SUGGEST THAT IRENE IS ENCOUNTERING LIGHT TO MODERATE
SOUTHWESTERLY VERTICAL WIND SHEAR.  THIS...ALONG WITH THE CURRENT
CYCLONE STRUCTURE AND DRY AIR ADVECTING TOWARD THE HURRICANE IN
WATER VAPOR IMAGERY...ARGUE AGAINST SIGNIFICANT STRENGTHENING....
AND INDEED THE INTENSITY GUIDANCE SHOWS LITTLE CHANGE IN STRENGTH 
BEFORE LANDFALL.  ON THE OTHER HAND...THE EYEWALL CONVECTION IS
CURRENTLY STRONG...AND THE SEA SURFACE TEMPERATURES ALONG THE
FORECAST TRACK ARE 28-29C.  THIS SUGGESTS SOME MODEST STRENGTHENING
IS POSSIBLE.  IRENE IS EXPECTED TO BE NEAR THE CATEGORY 2/3
BOUNDARY WHEN IT REACHES THE VICINITY OF THE OUTER BANKS...AND
SLOWLY WEAKEN AFTER THAT. AFTER MOVING INTO NEW ENGLAND...IRENE
SHOULD WEAKEN QUICKLY AS IT UNDERGOES EXTRATROPICAL TRANSITION.

IRENE REMAINS A VERY LARGE TROPICAL CYCLONE.  THE WIND RADII HAVE
BEEN ADJUSTED BASED ON AIRCRAFT DATA AND AN ASCAT OVERPASS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/0900Z 29.3N  77.2W   95 KT 110 MPH
 12H  26/1800Z 31.0N  77.2W  100 KT 115 MPH
 24H  27/0600Z 33.1N  76.9W  100 KT 115 MPH
 36H  27/1800Z 35.3N  76.1W  105 KT 120 MPH
 48H  28/0600Z 37.8N  75.0W   85 KT 100 MPH
 72H  29/0600Z 45.0N  70.4W   55 KT  65 MPH...INLAND
 96H  30/0600Z 53.0N  61.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  31/0600Z 58.5N  44.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BEVEN
 

WTNT44 KNHC 261446
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  25
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 AM EDT FRI AUG 26 2011
 
DATA FROM NOAA AND AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
SUGGEST THE INTENSITY OF IRENE IS SLIGHTLY LOWER.  ALTHOUGH PEAK
FLIGHT-LEVEL WINDS AT 700 MB WERE 111 KT...SFMR AND DROPSONDE
OBSERVATIONS INDICATED THAT A HIGHER-THAN-TYPICAL REDUCTION OF THE
WIND FROM FLIGHT-LEVEL TO THE SURFACE APPLIES...AND THE INITIAL
INTENSITY IS REDUCED TO 90 KT.  GIVEN THE CURRENT STORM STRUCTURE
AND PREDICTED ENVIRONMENTAL FACTORS...LITTLE CHANGE IN STRENGTH IS
EXPECTED DURING THE NEXT 12 TO 24 HOURS.  AFTER PASSING NORTH
CAROLINA...SOUTHWESTERLY SHEAR IS FORECAST TO INCREASE AND SEA
SURFACE TEMPERATURES WILL BE GRADUALLY DECREASING.  THIS SHOULD
RESULT IN GRADUAL WEAKENING OF THE CYCLONE AS IT MOVES NEAR THE
MID-ATLANTIC COAST.  HOWEVER...IRENE IS EXPECTED TO REMAIN A LARGE
AND DANGEROUS TROPICAL CYCLONE AND HAS THE POTENTIAL TO PRODUCE
DAMAGING WINDS...STORM SURGE FLOODING...AND EXTREMELY HEAVY RAINS
ALMOST ANYWHERE FROM EASTERN NORTH CAROLINA NORTHWARD THROUGH NEW
ENGLAND.
 
IRENE IS MOVING NORTHWARD OR 360/12 KT.  THERE HAS BEEN NO CHANGE
TO THE FORECAST PHILOSOPHY.  IRENE SHOULD MOVE NORTHWARD FOR ANOTHER
12 HOURS OR SO....FOLLOWED BY A GRADUAL TURN TO THE NORTH-NORTHEAST
AS IT MOVES ALONG THE EAST COAST OF THE UNITED STATES.  THE TRACK
GUIDANCE IS IN GOOD AGREEMENT ON THIS SCENARIO AND NO CHANGE WAS
REQUIRED FROM THE PREVIOUS NHC FORECAST THROUGH 72 HOURS.
 
ONLY A SMALL ADJUSTMENT WAS MADE TO THE HURRICANE WARNING ON THIS
ADVISORY.  IT IS ANTICIPATED THAT THE HURRICANE WARNING AND WATCH
AREAS WILL NEED TO BE EXTENDED NORTHWARD ALONG THE U.S. EAST COAST
THIS AFTERNOON.
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/1500Z 30.7N  77.3W   90 KT 105 MPH
 12H  27/0000Z 32.2N  77.1W   90 KT 105 MPH
 24H  27/1200Z 34.4N  76.6W   90 KT 105 MPH
 36H  28/0000Z 36.7N  75.6W   85 KT 100 MPH
 48H  28/1200Z 39.5N  74.1W   75 KT  85 MPH
 72H  29/1200Z 47.5N  68.8W   55 KT  65 MPH...INLAND
 96H  30/1200Z 55.5N  57.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  31/1200Z 59.0N  38.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BROWN/BLAKE
 

WTNT44 KNHC 262049
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  26
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 PM EDT FRI AUG 26 2011
 
THE AIRCRAFT DID NOT FIND ANY HIGHER WINDS AFTER THE RELEASE OF THE
PREVIOUS ADVISORY. IN FACT...DATA FROM NEAR THE CONCLUSION OF THE
FLIGHT SUPPORT A SLIGHT LOWER INITIAL INTENSITY. THE AIRCRAFT DID
REPORT HURRICANE-FORCE WINDS AT FLIGHT LEVEL AND SFMR WINDS OF
50-55 KT 135 N MI EAST OF THE CENTER...SHOWING THE LARGE SIZE OF
THE WIND FIELD. BUOY OBSERVATIONS AND DATA FROM AN EARLIER ASCAT
PASS SHOW THAT THE TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD ABOUT
225-250 N MI OVER THE EASTERN SEMICIRCLE. RECENT MICROWAVE DATA AND
OBSERVATIONS FROM THE AIRCRAFT INDICATE THAT THE INNER CORE HAS
ERODED. ALTHOUGH IRENE WILL BE MOVING OVER WARM WATER DURING THE
NEXT 12-18 HOURS...THE LACK OF AN INNER CORE WILL LIKELY PRECLUDE
ANY RESTRENGTHENING. ALTHOUGH NOT SHOWN IN THE OFFICIAL
FORECAST...IRENE COULD WEAKEN JUST BELOW HURRICANE STRENGTH BEFORE
REACHING SOUTHERN NEW ENGLAND. HOWEVER...IMPACTS FROM THIS LARGE
TROPICAL CYCLONE WILL NOT BE VERY DIFFERENT IF IT IS A STRONG
TROPICAL STORM OR LOW-END HURRICANE. IRENE HAS THE POTENTIAL TO
PRODUCE DAMAGING WINDS...STORM SURGE FLOODING...AND EXTREMELY HEAVY
RAINS ALMOST ANYWHERE FROM EASTERN NORTH CAROLINA NORTHWARD THROUGH
NEW ENGLAND.  

IRENE IS STILL MOVING NORTHWARD OR 360/12 KT. IRENE IS EXPECTED TO
TURN NORTH-NORTHEASTWARD TONIGHT AND CONTINUE ON THAT HEADING UP
THE EAST COAST...AND BE MOVING AT ABOUT 15-17 KT AS IT APPROACHES
LONG ISLAND...MUCH SLOWER THAN NORMAL FOR STORMS IN THIS
AREA...WHICH WILL PRODUCE EXTENDED PERIODS OF TROPICAL STORM AND
HURRICANE-FORCE WINDS IN MANY AREAS. THE MODELS HAVE BEEN VERY
CONSISTENT ON THE FUTURE TRACK OF IRENE OVER THE LAST SEVERAL
CYCLES. THE NEW TRACK FORECAST IS VERY SIMILAR TO THE PREVIOUS
ADVISORY AND LIES BETWEEN THE GFS AND ECMWF.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/2100Z 31.7N  77.4W   85 KT 100 MPH
 12H  27/0600Z 33.4N  77.1W   80 KT  90 MPH
 24H  27/1800Z 35.5N  76.3W   75 KT  85 MPH...INLAND
 36H  28/0600Z 38.2N  75.0W   70 KT  80 MPH...OVER WATER
 48H  28/1800Z 41.8N  73.0W   60 KT  70 MPH...INLAND
 72H  29/1800Z 50.5N  65.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  30/1800Z 56.5N  51.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  31/1800Z 58.0N  32.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BROWN/CANGIALOSI
 

WTNT44 KNHC 270258
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  27
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 PM EDT FRI AUG 26 2011
 
AIR FORCE AND NOAA HURRICANE HUNTER AIRCRAFT LATE THIS AFTERNOON AND
EARLY EVENING HAVE FOUND SURFACE PRESSURES OF 950-951 MB AND
FLIGHT-LEVEL WINDS RANGING FROM 99 KT TO 108 KT IN THE SOUTHEAST
QUADRANT OF IRENE. HOWEVER...SFMR SURFACE WINDS HAVE BEEN MUCH
LOWER THAN THE STANDARD 90 PERCENT REDUCTION FACTOR TYPICALLY
YIELDS. THIS DISPARITY IS LIKELY DUE TO THE LACK OF SIGNIFICANT
CONVECTION OVER THE SOUTHERN SEMICIRCLE. NOAA DOPPLER RADAR DATA
FROM WILMINGTON AND MOREHEAD CITY HAVE BEEN INDICATING VIGOROUS
CONVECTION REDEVELOPING NORTH AND EAST OF THE RAGGED EYE...WITH
DOPPLER VELOCITIES OF 90 KT OR GREATER AT ALTITUDE ABOVE 15000
FEET. BASED ON THE RADAR DATA AND THE POSSIBILITY THAT THE STRONGER
FLIGHT-LEVEL WINDS COULD EVENTUALLY WORK INTO NORTHEAST QUADRANT OF
IRENE...THE INITIAL INTENSITY IS BEING HELD AT 85 KT.

RADAR AND RECON FIXES INDICATE IRENE HAS MADE THE LONG-FORECAST TURN
TOWARD THE NORTH-NORTHEAST NOW AND IS MOVING AT 020/12 KT. IRENE IS
CAUGHT BETWEEN A BROAD SUBTROPICAL RIDGE TO THE EAST AND AN
APPROACHING SHORTWAVE TROUGH CURRENTLY MOVING EASTWARD OVER THE
GREAT LAKES AND OHIO VALLEY. THE HURRICANE IS EXPECTED TO CONTINUE
MOVING NORTH-NORTHEASTWARD FOR THE NEXT 24 HOURS OR SO AS THE RIDGE
TO THE EAST AMPLIFIES NORTHWARD. THEREAFTER...THE CYCLONE SHOULD
ACCELERATE TO THE NORTHEAST AS IT GETS CAUGHT UP IN DEEP-LAYER
SOUTHWESTERLY FLOW AHEAD OF THE SHORTWAVE TROUGH. THE FORECAST
TRACK HAS ONLY BEEN NUDGED SLIGHTLY EASTWARD OF THE PREVIOUS TRACK
THROUGH 36 HOURS DUE TO THE MORE EASTWARD INITIAL POSITION.
HOWEVER...ALL OF THE MODELS SUGGEST THAT SOME SLIGHT MID-LEVEL
RIDGING WILL OCCUR ACROSS SOUTHERN NEW ENGLAND AND THE MID-ATLANTIC
STATES DURING THE NEXT 12-24 HOURS...WHICH SHOULD ACT TO KEEP IRENE
CLOSE TO THE COASTS OF NEW JERSEY AND THE DELMARVA PENINSULA. THE
TRACK FORECAST LIES DOWN THE MIDDLE OF THE NHC GUIDANCE ENVELOPE
AND IS A BLEND OF THE GFS AND ECMWF MODEL TRACKS.

IRENE IS EXPECTED TO REMAIN OVER SSTS GREATER THAN 28C UNTIL
LANDFALL ALONG THE NORTH CAROLINA OUTER BANKS IN 12-18 HOURS. THIS
SHOULD ALLOW THE CYCLONE TO MAINTAIN ITS CURRENT INTENSITY OR ONLY
WEAKEN SLIGHTLY. AFTER LANDFALL...HOWEVER...LAND INTERACTION...
COOLER WATER...AND GRADUALLY INCREASING SOUTHWESTERLY VERTICAL WIND
SHEAR IS EXPECTED TO INDUCE STEADY WEAKENING. ALTHOUGH A STATIONARY
FRONT CURRENTLY LIES ACROSS SOUTHERN NEW ENGLAND...THIS FEATURE IS
EXPECTED TO LIFT NORTHWARD DUE TO THE VERY LARGE CIRCULATION OF
IRENE. THIS SHOULD DELAY EXTRATROPICAL TRANSITION UNTIL IRENE IS
OVER MAINE OR SOUTHEASTERN CANADA. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0300Z 32.6N  76.9W   85 KT 100 MPH
 12H  27/1200Z 34.2N  76.4W   80 KT  90 MPH
 24H  28/0000Z 36.7N  75.5W   75 KT  85 MPH
 36H  28/1200Z 39.8N  74.0W   70 KT  80 MPH
 48H  29/0000Z 43.8N  71.3W   60 KT  70 MPH...INLAND
 72H  30/0000Z 52.0N  62.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  31/0000Z 56.5N  46.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  01/0000Z 57.5N  26.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER STEWART
 

WTNT44 KNHC 270857
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  28
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 AM EDT SAT AUG 27 2011
 
SATELLITE IMAGERY AND COASTAL RADAR DATA SHOW THAT IRENE HAS LOST
SOME ORGANIZATION THIS MORNING.  THE CLOUD TOPS HAVE WARMED
SIGNIFICANTLY IN THE WESTERN SEMICIRCLE...AND THERE IS A LACK OF
CONVECTIVE BANDING IN THE SOUTHWESTERN QUADRANT IN THE RADAR DATA.
THIS SUGGESTS THAT DRY AIR SEEN IN WATER VAPOR IMAGERY TO THE WEST
OF IRENE IS STARTING TO ENTRAIN INTO THE HURRICANE.  AN AIR FORCE
RESERVE HURRICANE HUNTER AIRCRAFT CONTINUES TO OBSERVE 90-100 KT
WINDS AT 700 MB OVER THE EASTERN SEMICIRCLE.  HOWEVER...THE HIGHEST
SURFACE WIND ESTIMATES FROM THE SFMR HAVE ONLY BEEN 70-75 KT.  THE
INITIAL INTENSITY IS REDUCED TO 80 KT...AND THIS COULD BE A LITTLE
GENEROUS.  DESPITE THE DECREASE IN CONVECTIVE ORGANIZATION...THE
AIRCRAFT REPORTS THAT THE CENTRAL PRESSURE REMAINS NEAR 952 MB.

THE INITIAL MOTION IS 020/12.  IRENE IS WEST OF THE SUBTROPICAL
RIDGE...WITH WATER VAPOR IMAGERY SHOWING A MID/UPPER-LEVEL
SHORTWAVE TROUGH IN THE WESTERLIES MOVING ACROSS THE GREAT LAKES. 
IRENE SHOULD CONTINUE TO MOVE NORTH-NORTHEASTWARD INTO THE
WESTERLIES DURING THE NEXT 36-48 HOURS...WITH THE CENTER MOVING
OVER EASTERN NORTH CAROLINA...OVER OR NEAR THE COAST OF THE
MID-ATLANTIC STATES...AND THEN OVER NEW ENGLAND.  AFTER 48 HOURS...
THE CYCLONE SHOULD TURN NORTHEASTWARD AND THEN EAST-NORTHEASTWARD
WITH AN INCREASE IN FORWARD SPEED AS IT REACHES THE CORE OF THE
WESTERLIES.  THE NEW FORECAST TRACK IS AN UPDATE OF THE PREVIOUS
TRACK AND LIES IN THE CENTER OF THE GUIDANCE ENVELOPE.

LAND INTERACTION...DRY AIR ENTRAINMENT...AND INCREASING VERTICAL
WIND SHEAR SHOULD CAUSE IRENE TO WEAKEN AS IT MOVES ALONG THE U.S.
EAST COAST.  HOWEVER...THE CYCLONE IS EXPECTED TO REMAIN A
HURRICANE WITH A VERY LARGE WIND FIELD UNTIL AFTER LANDFALL IN NEW
ENGLAND.  EXTRATROPICAL TRANSITION SHOULD OCCUR AFTER THE NEW
ENGLAND LANDFALL...WITH IRENE GRADUALLY WEAKENING FROM 48-120 HR.

THE RADAR PRESENTATION OF THE CENTER OF IRENE HAS DECREASED TO THE
POINT THAT WE WILL BE REVERTING TO THREE-HOURLY INTERMEDIATE
ADVISORIES.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0900Z 34.1N  76.5W   80 KT  90 MPH
 12H  27/1800Z 35.7N  75.8W   75 KT  85 MPH...INLAND
 24H  28/0600Z 38.4N  74.6W   70 KT  80 MPH...OVER WATER
 36H  28/1800Z 41.9N  72.7W   65 KT  75 MPH...INLAND
 48H  29/0600Z 46.3N  69.6W   50 KT  60 MPH...POST-TROP/EXTRATROP
 72H  30/0600Z 54.0N  59.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  31/0600Z 57.0N  41.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  01/0600Z 58.0N  23.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BEVEN
 

WTNT44 KNHC 271449
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  29
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 AM EDT SAT AUG 27 2011
 
NATIONAL WEATHER SERVICE DOPPLER RADAR AND SURFACE OBSERVATIONS
INDICATE THAT IRENE MADE LANDFALL AROUND 1130 UTC JUST WEST OF CAPE
LOOKOUT NORTH CAROLINA.  THE ESTIMATED INTENSITY AT LANDFALL WAS
75 KT.  THIS WAS BASED ON A PEAK FLIGHT-LEVEL WIND OF 98 KT AND A
SFMR SURFACE WIND OF 69 KT.  A DROPSONDE RELEASED BY A NOAA
AIRCRAFT MEASURED A MINIMUM PRESSURE OF 951 MB AROUND THE TIME
OF LANDFALL.  THE INITIAL INTENSITY WILL REMAIN 75 KT.
 
IRENE MOVED ALMOST DUE NORTHWARD BETWEEN 0600 AND 1200 UTC...BUT
HAS WOBBLED BACK TO THE RIGHT SINCE THAT TIME.  SMOOTHING THROUGH
THESE TEMPORARY CHANGES IN HEADING YIELDS AN INITIAL MOTION
ESTIMATE OF 015/13 KT.  IRENE SHOULD CONTINUE TO MOVE
NORTH-NORTHEASTWARD BETWEEN A MID-LEVEL RIDGE OVER THE EAST-CENTRAL
ATLANTIC AND A TROUGH PASSING OVER THE GREAT LAKES REGION.  AFTER
48 HOURS...THE CYCLONE SHOULD REACH THE MID-LATITUDE WESTERLIES AND
TURN NORTHEASTWARD THEN EAST-NORTHEASTWARD.  THE MODELS ARE TIGHTLY
CLUSTERED FOR THE FIRST 2-3 DAYS OF THE FORECAST PERIOD AND THERE IS
HIGH CONFIDENCE IN THE TRACK FORECAST INTO EASTERN CANADA.  THE
UPDATED NHC FORECAST HAS BEEN NUDGED WESTWARD TO BE IN BETTER
AGREEMENT WITH LATEST ECMWF AND GFS SOLUTIONS.
 
IRENE IS FORECAST TO GRADUALLY WEAKEN AS IT MOVES ALONG THE EAST
COAST OF THE UNITED STATES DUE TO LAND INTERACTION...DRY AIR
ENTRAINMENT...AND INCREASING SOUTHWESTERLY SHEAR.  IF THE CENTER OF
IRENE MOVES MORE OVER LAND THAN FORECAST DURING THE NEXT 12-24
HOURS...IT COULD BE SLIGHTLY WEAKER THAN PREDICTED.  WHETHER IRENE
IS A STRONG TROPICAL STORM OR HURRICANE OVER NEW ENGLAND WILL MAKE
LITTLE DIFFERENCE IN THE EXPECTED IMPACTS OF DAMAGING WINDS...A
DANGEROUS STORM SURGE...AND FLOODING RAINS.

FORECAST POSITIONS AND MAX WINDS
 
INIT  27/1500Z 35.2N  76.4W   75 KT  85 MPH
 12H  28/0000Z 37.2N  75.5W   70 KT  80 MPH
 24H  28/1200Z 40.3N  73.9W   65 KT  75 MPH
 36H  29/0000Z 44.3N  71.5W   60 KT  70 MPH...INLAND
 48H  29/1200Z 48.7N  67.7W   45 KT  50 MPH...POST-TROP/EXTRATROP
 72H  30/1200Z 55.5N  55.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  31/1200Z 58.0N  36.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  01/1200Z 59.0N  26.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BROWN
 

WTNT44 KNHC 272057
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  30
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 PM EDT SAT AUG 27 2011
 
THE CENTER OF IRENE HAS BEEN MOVING ACROSS EASTERN NORTH CAROLINA
THIS AFTERNOON...AND THE RADAR PRESENTATION OF THE INNER CORE
ACTUALLY IMPROVED FOR A FEW HOURS.  SINCE THAT TIME...THE RAGGED
EYE HAS FILLED IN BUT THE CENTER REMAINS WELL DEFINED ON
RADAR...WHICH WARRANTS A RETURN TO TWO-HOURLY INTERMEDIATE
ADVISORIES.  AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
REPORTED PEAK FLIGHT-LEVEL WINDS OF 85-90 KT TO THE EAST OF THE
CENTER DURING THE PAST FEW HOURS...AND A VERY RECENT CENTER DROP
MEASURED A MINIMUM PRESSURE OF 950 MB.  THERE HAVE NOT BEEN ANY
RECENT SFMR DATA...BUT BASED ON THE EARLIER SHARP DISCREPANCY
BETWEEN THE FLIGHT-LEVEL AND SURFACE WINDS...THE INITIAL INTENSITY
IS REDUCED TO 70 KT.  A SLOW WEAKENING IS EXPECTED AS IRENE MOVES
ALONG THE COAST OF THE MID-ATLANTIC STATES DUE TO LAND
INTERACTION...COLDER WATERS...DRY AIR ENTRAINMENT...AND INCREASING
SOUTHWESTERLY SHEAR.  BECAUSE THE LARGE WIND FIELD WILL TAKE TIME
TO SPIN DOWN...HOWEVER...IRENE IS STILL EXPECTED TO REACH THE NEW
YORK AREA AT OR NEAR HURRICANE STRENGTH.

MORE SO THAN WITH MOST STORMS...THE WINDS WITH IRENE INCREASE
SHARPLY WITH HEIGHT ABOVE THE SURFACE.  AS IRENE MOVES THROUGH
AREAS WITH HIGH-RISE STRUCTURES...THESE STRUCTURES WILL EXPERIENCE
WINDS SIGNIFICANTLY STRONGER THAN INDICATED BY THE ADVISORY
INTENSITY.  WINDS AT THE 30-STORY LEVEL WILL LIKELY BE 20 PERCENT
HIGHER THAN AT THE SURFACE...AND WINDS 80-100 STORIES UP COULD BE
ABOUT 30 PERCENT HIGHER THAN AT THE SURFACE.
 
THE CENTER CONTINUED NORTHWARD FOR A SHORT PERIOD OF TIME AFTER THE
RELEASE OF THE PREVIOUS ADVISORY BUT HAS RESUMED A NORTHEASTWARD
MOTION OF ABOUT 015/11. IRENE IS FORECAST TO MOVE NORTH-
NORTHEASTWARD ALONG THE MID-ATLANTIC COAST TONIGHT AND OVER NEW
ENGLAND ON SUNDAY. AFTER THE CYCLONE BECOMES EXTRATROPICAL IN 36-48
HOURS IT SHOULD TURN NORTHEASTWARD THEN EAST-NORTHEASTWARD IN THE
MID-LATITUDE WESTERLIES. THE NEW TRACK FORECAST IS UNCHANGED FROM
THE PREVIOUS ADVISORY. 

NOTE THAT ESTIMATES OF STORM TOTAL RAINFALL HAVE BEEN INCREASED WITH
THIS ADVISORY...TO 20 INCHES.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/2100Z 36.2N  76.0W   70 KT  80 MPH
 12H  28/0600Z 38.1N  75.1W   65 KT  75 MPH
 24H  28/1800Z 41.7N  73.2W   60 KT  70 MPH...INLAND
 36H  29/0600Z 46.2N  70.2W   45 KT  50 MPH...POST-TROP/EXTRATROP
 48H  29/1800Z 50.7N  66.3W   45 KT  50 MPH...POST-TROP/EXTRATROP
 72H  30/1800Z 56.5N  53.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  31/1800Z 59.0N  37.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  01/1800Z 61.0N  26.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BROWN/FRANKLIN
 

WTNT44 KNHC 280257
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  31
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 PM EDT SAT AUG 27 2011
 
IRENE HAS CHANGED LITTLE IN APPEARANCE IN SATELLITE IMAGERY...BUT
THE RADAR DEPICTION HAS DEGRADED OVER THE PAST FEW HOURS.   AN AIR
FORCE RECONNAISSANCE AIRCRAFT INVESTIGATING THE HURRICANE THIS
EVENING HAS FOUND 700 MB FLIGHT-LEVEL WINDS OF 92 KT AND SFMR WINDS
OF 66 KT IN A SMALL AREA MORE THAN 100 NMI EAST OF THE CENTER.
BASED ON THIS INFORMATION...THE INTENSITY OF IRENE IS BEING
MAINTAINED AT 70 KT FOR THIS ADVISORY. IT SHOULD BE NOTED THAT THE
WIND FIELD GRAPHICS BASED ON THE FOUR-QUADRANT RADII WILL DEPICT AN
UNREALISTICALLY LARGE AREA OF HURRICANE-FORCE WINDS.
 
THE INITIAL MOTION ESTIMATE IS NOW 020/14...AND IRENE REMAINS ON
TRACK. IRENE IS EXPECTED TO CONTINUE MOVING NORTH-NORTHEASTWARD
AHEAD OF AN EASTWARD-MOVING SHORTWAVE TROUGH...AND SKIRT THE
MID-ATLANTIC COAST TONIGHT AND EARLY SUNDAY MORNING...AND MOVE OVER
NEW ENGLAND BY SUNDAY AFTERNOON. AFTER IRENE BECOMES A
POST-TROPICAL/EXTRATROPICAL LOW BY 36 HOURS...THE CYCLONE SHOULD
GRADUALLY TURN NORTHEASTWARD THEN EAST-NORTHEASTWARD AS IT MOVES
INTO THE DEEP-LAYER MID-LATITUDE WESTERLIES. THE FORECAST TRACK IS
JUST AN EXTENSION OF THE PREVIOUS ADVISORY AND REMAINS IN THE
MIDDLE OF THE TIGHTLY PACKED NHC MODEL GUIDANCE.

IRENE WILL BE MOVING OVER PROGRESSIVELY COOLER WATER UNTIL LANDFALL
OCCURS ON LONG ISLAND...WHICH WOULD NORMALLY RESULT IN SIGNIFICANT
WEAKENING OF MOST HURRICANES. HOWEVER...DUE TO THE UNUSUALLY LARGE
WIND FIELD OF IRENE...ONLY SLOW WEAKENING IS EXPECTED THROUGHOUT
THE FORECAST PERIOD...AND IT WILL ONLY TAKE MODEST CONVECTION TO
BRING DOWN STRONGER WINDS ALOFT TO THE SURFACE AS SUSTAINED
HURRICANE-FORCE WINDS OR GUSTS.

MORE SO THAN WITH MOST STORMS...THE WINDS WITH IRENE INCREASE
SHARPLY WITH HEIGHT ABOVE THE SURFACE.  AS IRENE MOVES THROUGH
AREAS WITH HIGH-RISE STRUCTURES...THESE BUILDINGS COULD EXPERIENCE
WINDS SIGNIFICANTLY STRONGER THAN THE SURFACE WINDS.  WINDS AT THE
30-STORY LEVEL WILL LIKELY BE 20 PERCENT HIGHER THAN AT THE
SURFACE...AND WINDS 80-100 STORIES UP COULD BE ABOUT 30 PERCENT
HIGHER THAN AT THE SURFACE.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/0300Z 37.3N  75.4W   70 KT  80 MPH
 12H  28/1200Z 39.8N  74.1W   65 KT  75 MPH
 24H  29/0000Z 44.0N  71.8W   55 KT  65 MPH...INLAND
 36H  29/1200Z 48.5N  67.8W   45 KT  50 MPH...POST-TROP/EXTRATROP
 48H  30/0000Z 52.4N  62.8W   45 KT  50 MPH...POST-TROP/EXTRATROP
 72H  31/0000Z 57.7N  48.6W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  01/0000Z 60.0N  33.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  02/0000Z 61.2N  24.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER STEWART
 

WTNT44 KNHC 280842
TCDAT4
 
HURRICANE IRENE DISCUSSION NUMBER  32
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 AM EDT SUN AUG 28 2011
 
SATELLITE AND RADAR IMAGERY SHOW THAT DRY AIR IS NOW WRAPPING INTO
MUCH OF THE SOUTHERN SEMICIRCLE OF IRENE...AND THE CYCLONE IS
SLOWLY BEGINNING TO FILL AS MEASUREMENTS FROM THE AIR FORCE RESERVE
HURRICANE HUNTER AIRCRAFT SHOW THAT THE CENTRAL PRESSURE IS UP TO
958 MB.  BASED ON DROPSONDE AND SFMR DATA SHOWING THAT SURFACE
WINDS HAVE CONTINUED TO SLOWLY WEAKEN...THE INITIAL INTENSITY IS
LOWERED TO 65 KT FOR THIS ADVISORY.  DESPITE THE GRADUAL WEAKENING
OF THE CYCLONE...THE OUTER WIND FIELD CONTINUES TO EXPAND...WITH
34-KT WINDS OCCURRING FROM NEW YORK CITY SOUTHWARD TO NORTHEASTERN
NORTH CAROLINA.  IRENE IS EXPECTED TO REMAIN NEAR HURRICANE
STRENGTH UNTIL IT MOVES INTO SOUTHERN NEW ENGLAND LATER TODAY...
AND IT WILL ONLY TAKE MODEST CONVECTION TO BRING DOWN STRONGER WINDS
ALOFT TO THE SURFACE AS SUSTAINED HURRICANE-FORCE WINDS OR GUSTS. 
SLOW WEAKENING IS EXPECTED AFTER LANDFALL AS IRENE BECOMES A
POST-TROPICAL CYCLONE IN ABOUT 24 HOURS.
 
THE INITIAL MOTION ESTIMATE IS 020/16...AS IRENE CONTINUES TO
ACCELERATE TOWARD THE NORTH-NORTHEAST ON THE WESTERN SIDE OF THE
SUBTROPICAL RIDGE.  OVER THE NEXT DAY OR SO...IRENE WILL MERGE INTO
THE MID-LATITUDE WESTERLIES AND ACCELERATE NORTHEASTWARD OVER
EASTERN CANADA AND INTO THE NORTH ATLANTIC.  THE TRACK GUIDANCE
REMAINS TIGHTLY PACKED...BUT HAS SHIFTED A LITTLE TO THE LEFT IN
THE VERY SHORT TERM.  THE NEW NHC TRACK FORECAST HAS BEEN ADJUSTED
IN THAT DIRECTION AND IS CLOSE TO THE ECMWF THROUGH 24 HOURS. 
AFTER EXTRATROPICAL TRANSITION THE NHC FORECAST IS A BLEND OF THE
GFS...ECMWF...AND UKMET.
 
NOTE...MORE SO THAN WITH MOST STORMS...THE WINDS WITH IRENE INCREASE
SHARPLY WITH HEIGHT ABOVE THE SURFACE.  AS IRENE MOVES THROUGH
AREAS WITH HIGH-RISE STRUCTURES...THESE BUILDINGS COULD EXPERIENCE
WINDS SIGNIFICANTLY STRONGER THAN THE SURFACE WINDS.  WINDS AT THE
30-STORY LEVEL WILL LIKELY BE 20 PERCENT HIGHER THAN AT THE
SURFACE...AND WINDS 80-100 STORIES UP COULD BE ABOUT 30 PERCENT
HIGHER THAN AT THE SURFACE.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/0900Z 39.2N  74.5W   65 KT  75 MPH
 12H  28/1800Z 41.8N  73.2W   60 KT  70 MPH...INLAND
 24H  29/0600Z 46.0N  70.4W   55 KT  65 MPH...POST-TROP/EXTRATROP
 36H  29/1800Z 50.6N  66.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
 48H  30/0600Z 54.0N  59.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  31/0600Z 58.0N  44.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  01/0600Z 61.0N  31.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  02/0600Z 62.0N  28.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BRENNAN
 

WTNT44 KNHC 281458
TCDAT4
 
TROPICAL STORM IRENE DISCUSSION NUMBER  33
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 AM EDT SUN AUG 28 2011
 
SURFACE AND RADAR DATA INDICATE THAT THE CENTER OF IRENE IS MOVING
JUST TO THE WEST OF CONNECTICUT.  THE FORWARD MOTION HAS ACCELERATED
TO NEAR 020/23...AND SOME ADDITIONAL INCREASE IN FORWARD SPEED IS
EXPECTED AS THE STORM MOVES ON THE EAST SIDE OF A BROAD
MID-TROPOSPHERIC TROUGH OVER EASTERN NORTH AMERICA.  THE OFFICIAL
FORECAST IS SIMILAR TO...BUT SLIGHTLY WEST OF...THE PREVIOUS TRACK.

SURFACE SYNOPTIC DATA SUGGEST THAT THE MAXIMUM WINDS HAVE DECREASED
TO 50 KT.  CONTINUED GRADUAL WEAKENING WILL OCCUR AS THE SYSTEM
MOVES OVER LAND TODAY.  IN 12 HOURS...GLOBAL MODELS SHOW IRENE
BECOMING EMBEDDED WITHIN A BAROCLINIC ZONE SO THE FORECAST SHOWS
EXTRATROPICAL TRANSITION BY THAT TIME. 

SIGNIFICANTLY STRONGER WINDS ARE STILL POSSIBLE OVER HIGH-RISE
STRUCTURES AND AREAS OF ELEVATED TERRAIN. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/1500Z 41.4N  73.7W   50 KT  60 MPH
 12H  29/0000Z 44.5N  71.7W   50 KT  60 MPH...POST-TROP/EXTRATROP
 24H  29/1200Z 49.0N  68.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 36H  30/0000Z 53.0N  63.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 48H  30/1200Z 56.0N  56.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  31/1200Z 60.0N  38.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  01/1200Z 62.0N  29.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  02/1200Z 63.0N  27.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER PASCH
 

WTNT44 KNHC 282036
TCDAT4
 
TROPICAL STORM IRENE DISCUSSION NUMBER  34
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 PM EDT SUN AUG 28 2011
 
SURFACE OBSERVATIONS INDICATE THAT THE CENTER IS BECOMING ELONGATED
FROM SOUTHWEST TO NORTHEAST.  WSR-88D RADAR DATA SHOW THAT THE MAIN
AREA OF PRECIPITATION IS BECOMING DISPLACED WELL TO THE NORTH OF
THE CENTER.  THESE OBSERVATIONS SUGGEST THAT IRENE IS BEGINNING TO
LOSE TROPICAL CHARACTERISTICS...BUT WE WILL RETAIN THE SYSTEM AS A
TROPICAL CYCLONE FOR NOW.  IT IS LIKELY HOWEVER...THAT THE NEXT
ADVISORY PACKAGE WILL BE THE LAST.  AFTER THE CYCLONE BECOMES
EXTRATROPICAL...GLOBAL MODELS SUGGEST THAT THE SYSTEM WILL NOT
RESTRENGTHEN DUE TO BAROCLINIC FORCING...AND THIS IS REFLECTED IN
THE OFFICIAL FORECAST.
 
THE INITIAL MOTION CONTINUES TO BE NEAR 020/23.  IRENE OR ITS
POST-TROPICAL COUNTERPART WILL CONTINUE TO BE STEERED BY THE FLOW
ON THE EAST SIDE OF A BROAD MID-TROPOSPHERIC TROUGH FOR THE NEXT
DAY OR TWO.  AFTERWARDS THE CYCLONE SHOULD TURN EAST-NORTHEASTWARD
IN THE MID-LATITUDE WESTERLIES.  THE OFFICIAL FORECAST FOR THIS
ADVISORY IS SIMILAR TO THE PREVIOUS ONE AND IS A BLEND OF THE
LATEST GFS AND ECMWF SOLUTIONS.
 
SIGNIFICANTLY STRONGER WINDS ARE STILL POSSIBLE OVER HIGH-RISE
STRUCTURES AND AREAS OF ELEVATED TERRAIN.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/2100Z 42.7N  72.8W   45 KT  50 MPH
 12H  29/0600Z 46.5N  70.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
 24H  29/1800Z 50.8N  66.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
 36H  30/0600Z 54.5N  61.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 48H  30/1800Z 57.0N  55.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  31/1800Z 60.0N  35.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  01/1800Z 63.0N  28.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  02/1800Z 64.0N  30.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER PASCH
 

