WTNT41 KNHC 012047
TCDAT1
TROPICAL STORM ERIKA DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062009
500 PM EDT TUE SEP 01 2009
 
AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT HAS BEEN INVESTIGATING
THE LOW PRESSURE AREA EAST OF THE LEEWARD ISLANDS AND HAS FOUND A
MINIMUM PRESSURE OF ABOUT 1007 MB AND A CLOSED...ALBEIT...BROAD
CIRCULATION.  PEAK FLIGHT-LEVEL WINDS WERE 52 KT WITH SFMR DATA OF
ABOUT 45 KT.  THUS...TROPICAL STORM ERIKA HAS FORMED WITH AN
INITIAL INTENSITY OF 45 KT.
 
SATELLITE IMAGES SHOW THAT ERIKA IS EXPERIENCING MODERATE
SOUTHWESTERLY SHEAR WITH THE CENTER NEAR THE WESTERN EDGE OF THE
DEEP CONVECTION.  SOME STRENGTHENING OF THE STORM SEEMS POSSIBLE
DURING THE NEXT DAY OR TWO WHILE THE SSTS ARE WARM AND SHEAR
REMAINS MODERATE.  HOWEVER...IN ABOUT TWO DAYS...GLOBAL MODELS
SIGNIFICANTLY INCREASE THE SHEAR NEAR THE TROPICAL CYCLONE AS
UPPER-LEVEL WESTERLIES FROM A MID-OCEANIC TROUGH OVER THE WESTERN
ATLANTIC IMPINGE ON THE SYSTEM.  MOST OF THE GLOBAL MODELS SHOW
ERIKA WEAKENING AFTER TWO DAYS DUE TO THE SHEAR.  THE TWO BIG
OUTLIERS IN THE MODEL GUIDANCE ARE THE GFDL/HWRF...WHICH FORM AN
ANTICYCLONE NEAR ERIKA AND MAKE IT A HURRICANE. THE NHC FORECAST
WILL SHOW SLOW INTENSIFICATION OVER THE FIRST COUPLE OF DAYS...THEN
WEAKENING THEREAFTER AS THE SHEAR TAKES OVER. THE NHC FORECAST WILL
BE CONSERVATIVE AT THIS TIME...BUT IT IS OF NOTE THAT ALMOST ALL OF
THE RELIABLE INTENSITY GUIDANCE SHOW ERIKA EVENTUALLY BECOMING A
HURRICANE...DESPITE THE SHEAR.
 
THE INITIAL MOTION ESTIMATE IS 300/8...THOUGH THE CENTER APPEARS TO
HAVE DONE SOME REFORMATION SINCE YESTERDAY.  MID-LEVEL RIDGING
OVER THE WEST-CENTRAL ATLANTIC SHOULD CAUSE ERIKA TO MOVE ALONG
THAT GENERAL COURSE FOR THE NEXT COUPLE OF DAYS.  THEREAFTER...
THE STORM COULD TURN MORE TO THE NORTHWEST AS IT NEARS THE
SOUTHWESTERN PERIPHERY OF THE RIDGE.  THIS FORECAST IS RATHER
UNCERTAIN AS THE TRACK PROBABLY HAS A STRONG DEPENDENCE ON THE
FUTURE INTENSITY OF ERIKA.  A WEAKER SYSTEM WOULD LIKELY MOVE MORE
TO THE WEST...SIMILAR TO THE UKMET OR GFS MODELS.  HOWEVER...A
STRONGER SYSTEM WOULD LIKELY FEEL THE STRONG UPPER-LEVEL WINDS AND
MOVE MORE TO THE RIGHT...LIKE THE HWRF/GFDL.  THE OFFICIAL FORECAST
IS LEFT OF THE DYNAMICAL CONSENSUS DUE TO THE STRONG SHEAR FORECAST
IN THE LONGER-TERM.
 
BECAUSE OF THE PROXIMITY TO THE NORTHERN LEEWARD ISLANDS...TROPICAL
STORM WATCHES HAVE BEEN ISSUED IN THAT AREA. 

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      01/2100Z 17.2N  57.3W    45 KT
 12HR VT     02/0600Z 17.7N  58.2W    45 KT
 24HR VT     02/1800Z 18.4N  60.3W    50 KT
 36HR VT     03/0600Z 19.1N  62.0W    55 KT
 48HR VT     03/1800Z 19.8N  63.8W    60 KT
 72HR VT     04/1800Z 21.0N  66.5W    55 KT
 96HR VT     05/1800Z 23.0N  69.5W    50 KT
120HR VT     06/1800Z 25.0N  72.0W    45 KT
 
$$
FORECASTER BLAKE/FRANKLIN
 

WTNT41 KNHC 020246
TCDAT1
TROPICAL STORM ERIKA DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062009
1100 PM AST TUE SEP 01 2009
 
AN AIR FORCE RECONNAISSANCE PLANE HAS BEEN TRAVERSING ERIKA AND
FOUND THAT THE CENTER HAS MOVED VERY LITTLE DURING THE PAST SEVERAL
HOURS. THE CIRCULATION HAS BECOME BETTER ESTABLISHED AND THE
MINIMUM CENTRAL PRESSURE FROM A DROP WAS 1004 MB. THIS VALUE COULD
BE A LITTLE BIT LOWER SINCE THE DROP MEASURED 19 KNOTS AT THE
SURFACE. THE SFMR AND THE PLANE MEASURED 55 AND 50 KNOTS...
RESPECTIVELY...TO THE NORTHEAST OF THE CENTER. THEREFORE...THE
INITIAL INTENSITY IS SET AT 50 KNOTS. THERE HAS BEEN AN INCREASE IN
CONVECTION NEAR THE CENTER AND THERE ARE SOME INDICATIONS FROM THE
HIGH-CLOUD MOTION THAT THE SHEAR HAS LESSENED A LITTLE BIT. ERIKA
COULD STRENGTHEN SOME DURING THE NEXT DAY OR TWO. THEREAFTER...MOST
OF THE GLOBAL MODELS HAVE STRONG UPPER-LEVEL WESTERLY WINDS OVER
ERIKA...A PATTERN THAT IS NOT FAVORABLE FOR STRENGTHENING. IN
FACT...THE OFFICIAL FORECAST CALLS FOR WEAKENING DURING THAT PERIOD
AS OPPOSED TO THE GFDL AND HWRF THAT BOTH MAKE ERIKA A STRONG
HURRICANE.  

ERIKA HAS BEEN MOVING VERY LITTLE DURING THE PAST FEW HOURS...BUT
THIS COULD BE THE RESULT OF THE CYCLONE BEING IN ITS FORMATIVE
STAGE. ERIKA IS LOCATED ON THE SOUTHWESTERN EDGE OF THE
AZORES-BERMUDA HIGH AND THE CYCLONE SHOULD BEGIN TO MOVE TOWARD THE
WEST-NORTHWEST OR 300 DEGREES AT 7 KNOTS ON WEDNESDAY. BECAUSE THE
AZORES-BERMUDA HIGH IS FORECAST TO EXPAND WESTWARD A LITTLE
BIT...ERIKA SHOULD MAINTAIN THIS WEST-NORTHWEST TO NORTHWEST TRACK.
SINCE THE STEERING CURRENTS ARE NOT VERY STRONG....ERIKA SHOULD
MOVE SLOWLY. GUIDANCE IS NOT IN GOOD AGREEMENT AND THE CONFIDENCE
IN THE FORECAST TRACK IS LOW. BOTH THE UK AND THE GFS TAKE A MORE
WESTWARD TRACK WHILE THE OTHER MODELS SHOW A MORE NORTHWESTERLY
COMPONENT. THE OFFICIAL FORECAST IS VERY CLOSE TO THE CONSENSUS
WHICH IS CENTERED BETWEEN THESE TWO MODEL OPTIONS. 

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/0300Z 17.5N  57.6W    50 KT
 12HR VT     02/1200Z 18.0N  58.7W    55 KT
 24HR VT     03/0000Z 18.5N  60.2W    60 KT
 36HR VT     03/1200Z 19.0N  61.8W    60 KT
 48HR VT     04/0000Z 19.5N  63.2W    55 KT
 72HR VT     05/0000Z 21.0N  66.0W    50 KT
 96HR VT     06/0000Z 22.6N  68.4W    45 KT
120HR VT     07/0000Z 24.5N  71.0W    45 KT
 
$$
FORECASTER AVILA
 

WTNT41 KNHC 020859
TCDAT1
TROPICAL STORM ERIKA DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062009
500 AM AST WED SEP 02 2009
 
AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT HAS BEEN SEARCHING
FOR THE CENTER OF THE TROPICAL STORM OVER THE PAST FEW HOURS.  THE
CIRCULATION HAS BECOME QUITE DISORGANIZED...BUT IT APPEARS THAT THE
CENTER HAS REFORMED TO THE SOUTHWEST OF THE PREVIOUSLY ESTIMATED
TRACK.  HOWEVER THE FLIGHT-LEVEL WINDS SUGGEST THAT THERE MAY BE
MULTIPLE CENTERS...SO THE ADVISORY POSITION IS HIGHLY UNCERTAIN AND
PROBABLY REPRESENTS A MEAN CENTER...OR THE LOCATION OF THE
LOW-LEVEL VORTICITY MAXIMUM.  THE INITIAL MOTION...270/4...IS OF
COURSE ALSO HIGHLY UNCERTAIN.  TO MAINTAIN SOME CONTINUITY FROM THE
PREVIOUS FORECAST AND FOLLOWING THE TRACK GUIDANCE...A WEST-
NORTHWESTWARD TRACK IS PREDICTED TO RESUME.  ERIKA SHOULD BE
STEERED BY THE FLOW TO THE SOUTH OF A WEAK SUBTROPICAL RIDGE FOR A
COUPLE OF DAYS.  LATER IN THE FORECAST PERIOD...DYNAMICAL GUIDANCE
SHOWS A MORE NORTHWESTWARD MOTION FOR A STRONGER CYCLONE...E.G. THE
GFDL AND HWRF...AND A CONTINUED WEST-NORTHWESTWARD MOTION FOR A
WEAKER SYSTEM...E.G. THE GFS.  THIS IS A LOW-CONFIDENCE TRACK
FORECAST.
 
DATA FROM THE AIRCRAFT INDICATE THAT ERIKA HAS WEAKENED A LITTLE...
WHICH IS NOT SURPRISING CONSIDERING THE DISORGANIZED APPEARANCE OF
THE SYSTEM ON SATELLITE IMAGES.  MODERATE WESTERLY SHEAR HAS BEEN
DISRUPTING THE CYCLONE BUT THE SHEAR IS NOT EXPECTED TO BE STRONG
ENOUGH TO PREVENT SOME STRENGTHENING DURING THE NEXT DAY OR SO.
THEREAFTER...AN UPPER-TROPOSPHERIC TROUGH FARTHER TO THE WEST IS
LIKELY TO IMPART INCREASING SOUTHWESTERLY SHEAR ON ERIKA...WHICH
SHOULD INDUCE WEAKENING.  THE NHC INTENSITY FORECAST IS VERY
SIMILAR TO THE PREVIOUS OFFICIAL FORECASTS...BUT BELOW THE
CONSENSUS OF THE NUMERICAL INTENSITY GUIDANCE.  IT SHOULD BE NOTED
THAT SOME OF THESE NUMERICAL MODELS...SUCH AS THE HWRF AND GFDL...
HAVE SHOWN A HIGH BIAS FOR A COUPLE OF THIS YEAR'S ATLANTIC
TROPICAL CYCLONES.
 
GIVEN THE SOUTHWARD SHIFT IN THE TRACK...A TROPICAL STORM WARNING
HAS BEEN ISSUED FOR THE NORTHERN LEEWARD ISLANDS.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/0900Z 17.0N  59.0W    45 KT
 12HR VT     02/1800Z 17.3N  60.1W    50 KT
 24HR VT     03/0600Z 17.8N  61.5W    55 KT
 36HR VT     03/1800Z 18.4N  62.9W    55 KT
 48HR VT     04/0600Z 19.0N  64.3W    55 KT
 72HR VT     05/0600Z 20.3N  66.9W    50 KT
 96HR VT     06/0600Z 22.0N  69.5W    45 KT
120HR VT     07/0600Z 24.0N  72.0W    45 KT
 
$$
FORECASTER PASCH
 

WTNT41 KNHC 021447
TCDAT1
TROPICAL STORM ERIKA DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062009
1100 AM AST WED SEP 02 2009
 
VISIBLE SATELLITE IMAGES AND AIR FORCE RESERVE HURRICANE HUNTER
DATA SHOW THAT ERIKA IS A POORLY ORGANIZED SYSTEM.  THERE ARE
MULTIPLE SWIRLS APPARENT ON THE SATELLITE IMAGERY ROTATING IN THE
LARGER CIRCULATION ENVELOPE WITH A MEAN CENTER TO THE WEST OF THE
DEEP CONVECTION.  THE SFMR EARLIER REPORTED WINDS OF ABOUT 35
KT...WHICH IS IN GOOD AGREEMENT WITH SATELLITE INTENSITY
ESTIMATES...SO THAT VALUE WILL BE USED AS THE INITIAL INTENSITY.  

VERTICAL WIND SHEAR HAS INCREASED EARLIER THAN EXPECTED...WITH CIMSS
DIAGNOSING ABOUT 15-20 KT OF SHEAR. AT FIRST GLANCE...THE SHEAR DOES
NOT APPEAR TO BE TOO STRONG OVER THE SYSTEM WITH SOUTH OR
SOUTHEASTERLY WINDS REPORTED AT 200 MB OVER THE NORTHERN LEEWARD
ISLANDS. HOWEVER...UPPER-AIR DATA FROM GUADELOUPE AND ST. MAARTEN
SUGGEST THAT THE SHEAR IS PRIMARILY COMING FROM SOUTHWESTERLY WINDS
BETWEEN 300 MB-250 MB...AND THIS IS APPARENTLY UNDERCUTTING THE
OUTFLOW LAYERS AT 200 MB AND ABOVE.  MOST OF THE GLOBAL MODELS DO
NOT SHOW MUCH RELAXATION OF THIS SHEAR...AND ACTUALLY SHOW IT
INCREASING SIGNIFICANTLY IN A COUPLE OF DAYS.  DESPITE ALL THIS
SHEAR...ALL RELIABLE GUIDANCE RESTRENGTHENS THIS SYSTEM TO NEAR
HURRICANE STRENGTH IN A FEW DAYS.  THIS REINTENSIFICATION 
DOES NOT SEEM VERY LIKELY AND THE NHC FORECAST IS MUCH LOWER THAN
THE GUIDANCE.  GIVEN THE POSSIBLE SHEAR DURING THE FORECAST
PERIOD...IT WOULD NOT BE SURPRISING IF ERIKA DISSIPATED.

A 24-HOUR MOTION IS ABOUT 275/9. A WEST-NORTHWESTWARD TRACK IS
PREDICTED TO RESUME AS THE STORM MOVES TO THE SOUTH OF A WEAK
SUBTROPICAL RIDGE FOR A COUPLE OF DAYS. THIS RIDGE IS FORECAST TO
WEAKEN SOMEWHAT IN A FEW DAYS...AND A NORTHWESTWARD MOTION IS
POSSIBLE BY THE END OF THE FORECAST. THE OFFICIAL FORECAST HAS BEEN
SHIFTED LEFT OF THE PREVIOUS ONE AND IS LEFT OF THE DYNAMICAL
CONSENSUS DUE TO THE ANTICIPATION OF ERIKA REMAINING WEAK. IT
SHOULD BE EMPHASIZED THAT...OVERALL...THIS IS A LOW-CONFIDENCE
TRACK FORECAST.

TROPICAL STORM WATCHES COULD BE REQUIRED FOR THE U.S. AND BRITISH
VIRGIN ISLANDS AS WELL AS PUERTO RICO LATER TODAY.  
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/1500Z 16.5N  60.4W    35 KT
 12HR VT     03/0000Z 16.9N  61.5W    35 KT
 24HR VT     03/1200Z 17.4N  62.8W    40 KT
 36HR VT     04/0000Z 18.0N  64.2W    45 KT
 48HR VT     04/1200Z 18.6N  65.5W    40 KT
 72HR VT     05/1200Z 20.0N  68.5W    35 KT
 96HR VT     06/1200Z 21.5N  71.5W    30 KT
120HR VT     07/1200Z 23.5N  73.5W    30 KT
 
$$
FORECASTER BLAKE/FRANKLIN
 

WTNT41 KNHC 022045
TCDAT1
TROPICAL STORM ERIKA DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062009
500 PM AST WED SEP 02 2009
 
SATELLITE IMAGES SHOW THAT THE CIRCULATION OF ERIKA IS ELONGATED
FROM SOUTHWEST TO NORTHEAST...IN AGREEMENT WITH SURFACE OBSERVATIONS
FROM THE LESSER ANTILLES AND REPORTS FROM AN AIR FORCE HURRICANE
HUNTER AIRCRAFT.  THE SWIRL SOUTHWEST OF GUADELOUPE APPEARS TO BE
PART OF THIS ELONGATED CIRCULATION...BUT IS NOT THE MEAN CENTER OF
THE OVERALL CYCLONIC ENVELOPE.  AIRCRAFT DATA ALSO INDICATE THAT
ERIKA IS STILL A TROPICAL STORM.  PEAK FLIGHT LEVEL WINDS WERE 44
KT AND SFMR DATA WERE BETWEEN 35-40 KT.  HOWEVER THE STRONGEST
WINDS WERE NEAR A LARGE THUNDERSTORM COMPLEX WELL SOUTHEAST OF THE
CENTER AND NOT DIRECTLY ASSOCIATED WITH THE STORM CIRCULATION.  THE
INITIAL INTENSITY WILL BE HELD AT 35 KT FOR THIS ADVISORY.
 
ERIKA HAS A DIFFICULT ROAD AHEAD WITH INCREASING SHEAR LIKELY AS THE
STORM NEARS THE GREATER ANTILLES.  WHILE SOME INTENSIFICATION CAN
NOT BE RULED OUT IN THE NEXT DAY OR SO...ALL OF THE GLOBAL MODELS
SHOW A VERY HOSTILE ENVIRONMENT WITH 20-30 KT SOUTHWESTERLY WINDS
AT 250 MB OVER ERIKA.  THESE WINDS ARE FORECAST TO CONTINUE...OR
INCREASE...AS THE STORM MOVES NEAR HISPANIOLA.  ALTHOUGH MOST OF THE
INTENSITY GUIDANCE STILL SHOWS RESTRENGTHENING OF ERIKA...THE
GUIDANCE HAS COME DOWN QUITE A BIT FROM THIS MORNING.  THE NHC
FORECAST IS LOWER THAN THE PREVIOUS ONE...AND SHOWS DISSIPATION OF
THE TROPICAL CYCLONE BY 5 DAYS.  ONE ALTERNATIVE SOLUTION IS THAT
INTERACTION WITH HISPANIOLA CAUSES AN EVEN FASTER DEMISE OF ERIKA.
 
THE LONG-TERM MOTION OF THIS SYSTEM IS ABOUT 275/9.  DURING THE
NEXT SEVERAL DAYS...THE STORM SHOULD BE STEERED TO THE WEST OR
WEST-NORTHWEST PRIMARILY BY A RIDGE OVER THE WESTERN ATLANTIC.  THE
GLOBAL MODELS HAVE SHIFTED SOUTHWARD WITH THE TRACK FORECAST SINCE
THIS MORNING...PERHAPS DUE TO THE WEAKER INITIAL STATE OF ERIKA.
THE NHC FORECAST IS SHIFTED SOUTHWARD AS WELL...REMAINING WEST OF
THE MODEL CONSENSUS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/2100Z 16.4N  61.7W    35 KT
 12HR VT     03/0600Z 16.8N  62.9W    35 KT
 24HR VT     03/1800Z 17.4N  64.6W    35 KT
 36HR VT     04/0600Z 18.0N  66.4W    30 KT...INLAND
 48HR VT     04/1800Z 18.7N  67.9W    30 KT
 72HR VT     05/1800Z 20.0N  70.5W    25 KT
 96HR VT     06/1800Z 21.5N  73.5W    20 KT...REMNANT LOW
120HR VT     07/1800Z...DISSIPATED
 
$$
FORECASTER BLAKE/FRANKLIN
 

WTNT41 KNHC 030242
TCDAT1
TROPICAL STORM ERIKA DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062009
1100 PM AST WED SEP 02 2009
 
ERIKA IS BARELY A TROPICAL STORM. DATA FROM A RECONNAISSANCE PLANE A
FEW HOURS AGO AND OBSERVATIONS FROM THE LESSER ANTILLES INDICATE
THAT ERIKA IS VERY DISORGANIZED AND CONSISTS OF A BROAD ELONGATED
CYCLONIC CIRCULATION WITH TROPICAL STORM FORCE WINDS IN
SQUALLS...LIMITED TO A FEW SPOTS OVER THE EASTERN SEMICIRCLE. A NEW
CENTER COULD REFORM AT ANY TIME WITHIN THE LARGE GYRE. INFRARED
PICTURES SUGGEST THAT THERE IS UPPER-LEVEL OUTFLOW IN ALL
QUADRANTS...BUT THERE IS ALSO SHEAR CAUSED BY WINDS BELOW THE
CIRRUS CANOPY BECAUSE THE CENTER CONTINUES TO BE LOCATED ON THE
WESTERN EDGE OF A STRONG AREA OF CONVECTION. IT APPEARS THAT ERIKA
IS ON ITS WAY TO DEGENERATE INTO A TROUGH OF LOW PRESSURE OR REFORM
SOMEWHERE WITHIN THE CIRCULATION. GLOBAL MODELS ARE FORECASTING A
LITTLE MORE FAVORABLE ENVIRONMENT IN 12 TO 24 HOURS AND THAT IS THE
REASON THE OFFICIAL FORECAST CALLS FOR NO CHANGE IN INTENSITY
DURING THE NEXT 12 HOURS. THEREAFTER...THE COMBINATION OF VERY
HOSTILE UPPER-LEVEL WESTERLIES AND THE LAND MASS OF HISPANIOLA
ALONG THE PATH OF THE CYCLONE...WOULD RESULT IN WEAKENING. THE HWRF
IS THE ONLY MODEL THAT FORECAST ERIKA TO BECOME A STRONG HURRICANE
AND THIS IS HIGHLY UNLIKELY TO OCCUR.           

THE CENTER OF THE LARGE CIRCULATION ENVELOPE HAS BEEN MOVING
WESTWARD AT 7 KNOTS. THE CYCLONE SHOULD BE STEERED TOWARD THE
WEST-NORTHWEST DURING THE NEXT FEW DAYS AROUND THE SUBTROPICAL
RIDGE WHICH IS FORECAST TO BUILD WESTWARD BY THE GLOBAL MODELS.
THE TRACK GUIDANCE IS LIMITED SINCE VARIOUS MODELS WEAKEN THE
CYCLONE WITH TIME AND THE TRACKERS NO LONGER FOLLOW THE CENTER.
HOWEVER...THE AVAILABLE CONSENSUS ALSO SUGGESTS THAT ERIKA OR ITS
REMNANTS SHOULD MOVE TOWARD THE WEST-NORTHWEST UNTIL DISSIPATION
AND SO DOES THE OFFICIAL FORECAST.  
  
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      03/0300Z 16.1N  62.4W    35 KT
 12HR VT     03/1200Z 16.4N  63.8W    35 KT
 24HR VT     04/0000Z 17.0N  65.5W    30 KT
 36HR VT     04/1200Z 18.0N  67.0W    30 KT
 48HR VT     05/0000Z 18.5N  68.5W    30 KT...INLAND
 72HR VT     06/0000Z 20.0N  71.0W    25 KT...REMNANT LOW
 96HR VT     07/0000Z 22.0N  73.0W    20 KT...REMNANT LOW
120HR VT     08/0000Z...DISSIPATED
 
$$
FORECASTER AVILA
 

WTNT41 KNHC 030836
TCDAT1
TROPICAL STORM ERIKA DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062009
500 AM AST THU SEP 03 2009
 
ALTHOUGH THE HURRICANE HUNTERS FIXED A FLIGHT-LEVEL CENTER...THERE
ARE A FAIR NUMBER OF SURFACE OBSERVATIONS OVER THE NORTHEASTERN
CARIBBEAN SEA REGION...AND THESE SHOW THAT THE SURFACE CIRCULATION
IS AT BEST POORLY-DEFINED.  THE SYSTEM MAY BE OPENING UP INTO A
TROUGH ORIENTED FROM SOUTH-SOUTHWEST TO NORTH-NORTHEAST.  THERE
WERE A FEW 34 TO 37-KT SFMR SURFACE WIND READINGS SOME 40-75 N MI
NORTH AND NORTHEAST OF THE FLIGHT-LEVEL CENTER...SO THE INTENSITY
IS MAINTAINED AT 35 KT.  EVEN THOUGH THERE MAY NO LONGER BE A
DEFINITE SURFACE CENTER OF CIRCULATION...WE WILL MAINTAIN
ADVISORIES ON THE SYSTEM PENDING ADDITIONAL DATA FROM THE
RECONNAISSANCE AIRCRAFT AND VISIBLE IMAGERY.  RADIOSONDE DATA FROM
THE EASTERN CARIBBEAN SEA AREA SUGGEST THAT THE STORM HAS BEEN
EXPERIENCING WESTERLY SHEAR DUE TO FLOW AT ABOUT THE 250 MB
LEVEL...WHICH IS LIKELY JUST BELOW THE TROPICAL CYCLONE OUTFLOW
LAYER.  GLOBAL MODELS SHOW INCREASING WEST-SOUTHWESTERLY SHEAR OVER
ERIKA DURING THE NEXT COUPLE OF DAYS DUE TO STRENGTHENING
UPPER-TROPOSPHERIC WINDS.  IN SPITE OF THE STRONG SHEAR...THE GFDL
AND HWRF MODELS CONTINUE TO FORECAST THAT ERIKA WILL INTENSIFY
SIGNIFICANTLY.  THE SHIPS AND LGEM GUIDANCE ARE MUCH LESS
AGGRESSIVE...PARTICULARLY THE LATTER.  THE OFFICIAL INTENSITY
FORECAST IS THE SAME AS THAT FROM THE PREVIOUS ADVISORY AND
ANTICIPATES THAT THE TROPICAL CYCLONE WILL DISSIPATE BY 72
HOURS.

BECAUSE OF THE UNCERTAINTIES IN THE LOCATION...OR EXISTENCE...OF THE
SURFACE CENTER...THE INITIAL MOTION ESTIMATE OF 295/6 IS MORE OF AN
EDUCATED GUESS.  A WEAK MID-LEVEL RIDGE LIES TO THE NORTH OF ERIKA. 
AS THE MODELS BUILD THIS RIDGE SOMEWHAT DURING THE NEXT COUPLE OF
DAYS...A SLIGHT INCREASE IN FORWARD SPEED IS LIKELY.  LATER IN THE
PERIOD A MORE NORTHWESTWARD TRACK IS FORECAST AS THE CYCLONE NEARS
THE WESTERN PERIPHERY OF THE RIDGE.  THE OFFICIAL FORECAST IS
SHIFTED A LITTLE NORTH OF THE PREVIOUS ONE PRIMARILY DUE TO A
SLIGHT NORTHWARD RELOCATION OF THE INITIAL POSITION.

EVEN IF ERIKA LOSES ITS TROPICAL CYCLONE STATUS...IT COULD MAINTAIN
VIGOROUS DEEP CONVECTION WHICH WOULD PRODUCE VERY HEAVY RAINS OVER
THE NORTHERN LESSER ANTILLES AND PUERTO RICO.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      03/0900Z 16.5N  62.7W    35 KT
 12HR VT     03/1800Z 17.1N  64.1W    35 KT
 24HR VT     04/0600Z 17.9N  65.6W    30 KT
 36HR VT     04/1800Z 18.7N  67.1W    30 KT
 48HR VT     05/0600Z 19.5N  68.5W    30 KT
 72HR VT     06/0600Z 21.0N  70.8W    25 KT...REMNANT LOW
 96HR VT     07/0600Z 22.5N  73.0W    20 KT...REMNANT LOW
120HR VT     08/0600Z...DISSIPATED
 
$$
FORECASTER PASCH
 

WTNT41 KNHC 031437
TCDAT1
TROPICAL STORM ERIKA DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062009
1100 AM AST THU SEP 03 2009
 
DATA FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT SHOW THAT
ERIKA HAS MOVED VERY SLOWLY OVER THE PAST FEW HOURS...AND THAT THE
CENTER IS SOMEWHAT ELONGATED. THE AIRCRAFT ALSO REPORTED THAT THE
CENTRAL PRESSURE HAS COME UP A LITTLE...TO 1010 MB. THERE WERE A
FEW UN-FLAGGED SFMR READINGS OF WINDS NEAR TROPICAL-STORM FORCE IN
THE CONVECTION WELL EAST OF THE CENTER...SO THE INTENSITY IS HELD
AT 35 KT FOR THIS ADVISORY. THE 1200 UTC RADIOSONDE DATA STILL SHOW
WESTERLY AND SOUTHWESTERLY FLOW AT THE 250 MB LEVEL WEST OF
ERIKA...AND THE SAN JUAN RAOB SHOWS A RELATIVELY DRY MID- AND
UPPER-TROPOSPHERIC ENVIRONMENT AHEAD OF THE CYCLONE. ALL OF THIS
EVIDENCE...PLUS THE POTENTIAL FOR LAND INTERACTION...SUGGESTS THAT
ERIKA SHOULD SLOWLY WEAKEN THROUGH THE PERIOD. DESPITE THIS...
ALMOST ALL OF THE INTENSITY GUIDANCE KEEPS ERIKA AS AT LEAST A
TROPICAL STORM THROUGH THE FORECAST PERIOD. THE OFFICIAL FORECAST
IS SIMILAR TO THE PREVIOUS ADVISORY...HOLDING ERIKA AS A TROPICAL
STORM THROUGH 12 HOURS AND SLOWLY WEAKENING THE CYCLONE TO A
REMNANT LOW BY DAY 3.
 
AIRCRAFT DATA AND SURFACE OBSERVATIONS...INCLUDING DATA FROM NOAA
BUOY 42060...SUGGESTED THAT THE CENTER OF ERIKA WAS LOCATED BETWEEN
THE ISLAND OF ST. KITTS AND THE BUOY. HOWEVER...THESE DATA ALSO
SUGGEST THAT THE CENTER IS STILL NOT TERRIBLY WELL DEFINED. ERIKA
IS MOVING SLOWLY WEST-NORTHWESTWARD AROUND THE SOUTHERN PERIPHERY
OF THE ATLANTIC SUBTROPICAL RIDGE...AND THE INITIAL MOTION ESTIMATE
IS A RATHER UNCERTAIN 300/07. THE GLOBAL MODEL GUIDANCE SUGGESTS
THAT THE RIDGE WILL BUILD WESTWARD NORTH OF ERIKA...WHICH SHOULD
RESULT IN A SLIGHT INCREASE IN FORWARD SPEED IN NEXT DAY OR TWO.
THE OFFICIAL FORECAST HAS BEEN SHIFTED SLIGHTLY TO THE RIGHT...OR
NORTHWARD...TO ACCOUNT FOR THE INITIAL POSITION AND A SLIGHT SHIFT
IN THE MODEL CONSENSUS.
 
WHILE IT IS LIKELY THAT ANY TROPICAL STORM FORCE WINDS ARE OCCURRING
IN ISOLATED AREAS WELL EAST OF THE CENTER...THE NEW FORECAST TRACK
IS CLOSE ENOUGH TO THE VIRGIN ISLANDS AND PUERTO RICO IN THE NEXT
12 TO 24 HOURS TO REQUIRE THE ISSUANCE OF A TROPICAL STORM WARNING
FOR THOSE ISLANDS AT THIS TIME.
 
EVEN IF ERIKA LOSES ITS TROPICAL CYCLONE STATUS LATER IN THE
FORECAST PERIOD...IT COULD MAINTAIN VIGOROUS DEEP CONVECTION WHICH
WOULD PRODUCE VERY HEAVY RAINS ALONG ITS TRACK.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      03/1500Z 16.9N  63.5W    35 KT
 12HR VT     04/0000Z 17.5N  64.5W    35 KT
 24HR VT     04/1200Z 18.4N  66.1W    30 KT...INLAND
 36HR VT     05/0000Z 19.2N  67.5W    30 KT
 48HR VT     05/1200Z 20.0N  68.8W    30 KT
 72HR VT     06/1200Z 21.5N  71.0W    25 KT...REMNANT LOW
 96HR VT     07/1200Z 23.0N  73.5W    20 KT...REMNANT LOW
120HR VT     08/1200Z...DISSIPATED
 
$$
FORECASTER BRENNAN
 

WTNT41 KNHC 032038
TCDAT1
TROPICAL DEPRESSION ERIKA DISCUSSION NUMBER   9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062009
500 PM AST THU SEP 03 2009
 
THE CENTER OF ERIKA IS EXPOSED AS A LOW-LEVEL SWIRL MOVING OUT AHEAD
OF THE WANING DEEP CONVECTION OVER THE LEEWARD ISLANDS. THE AIR
FORCE RESERVE RECONNAISSANCE HURRICANE HUNTER AIRCRAFT FOUND A
MINIMUM PRESSURE OF 1007 MB...BUT WERE UNABLE TO FIND ANY WINDS TO
SUPPORT TROPICAL STORM STATUS. AS A RESULT...ERIKA IS DOWNGRADED TO
A TROPICAL DEPRESSION ON THIS ADVISORY.
 
THE INITIAL MOTION ESTIMATE IS 280/10...WELL TO THE SOUTH OF THE
PREVIOUS OFFICIAL FORECAST TRACK AND THE MAJORITY OF ALL THE MODEL
GUIDANCE. SINCE ERIKA SHOULD MOVE WITH THE LOW-LEVEL FLOW...THE
SHALLOW BAM MODEL WAS FOLLOWED CLOSELY FOR THE NEW FORECAST TRACK.
THIS FORECAST TURNS ERIKA TOWARD THE WEST-NORTHWEST...TAKING THE
CYCLONE OR ITS REMNANT LOW SOUTH OF PUERTO RICO AND OVER HISPANIOLA
...WHERE THE LOW-LEVEL CENTER WILL LIKELY DISSIPATE OVER THE RUGGED
TERRAIN IN 48 HOURS.
 
THE OFFICIAL FORECAST ASSUMES THAT ERIKA WILL HAVE A DIFFICULT TIME
SUSTAINING ANY DEEP CONVECTION AS IT MOVES INTO AN ENVIRONMENT OF
INCREASING SHEAR AND DRY AIR IN THE LOWER TO MID-TROPOSPHERE. ERIKA
IS MAINTAINED AS A TROPICAL DEPRESSION THROUGH 12 HOURS...AND IS
FORECAST TO BE A REMNANT LOW BY 24 HOURS....ALTHOUGH THIS COULD
OCCUR SOONER IF THE CONVECTION EAST OF THE LOW-LEVEL CENTER OVER
THE LEEWARD ISLANDS CONTINUES TO WEAKEN. IT IS ALSO POSSIBLE THAT
THE CENTER OF ERIKA COULD BECOME POORLY DEFINED AND THE CYCLONE
COULD DEVOLVE INTO A TROPICAL WAVE AT ANY TIME. EVEN IF ERIKA LOSES
TROPICAL CYCLONE STATUS...ITS REMNANTS COULD PRODUCE HEAVY RAINFALL
OVER THE GREATER ANTILLES.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      03/2100Z 16.7N  65.3W    30 KT
 12HR VT     04/0600Z 17.2N  66.8W    30 KT
 24HR VT     04/1800Z 18.1N  68.6W    25 KT...REMNANT LOW
 36HR VT     05/0600Z 18.9N  70.3W    20 KT...REMNANT LOW
 48HR VT     05/1800Z 19.5N  72.2W    20 KT...DISSIPATING INLAND
 72HR VT     06/1800Z...DISSIPATED
 
$$
FORECASTER BRENNAN
 

WTNT41 KNHC 040232
TCDAT1
TROPICAL DEPRESSION ERIKA DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062009
1100 PM AST THU SEP 03 2009
 
ERIKA CONSISTS OF A TIGHT SWIRL OF LOW CLOUDS ACCOMPANIED BY A SMALL
AREA OF DEEP CONVECTION TO THE SOUTHEAST. THIS FEATURE IS CURRENTLY
OBSERVED ON SAN JUAN PUERTO RICO RADAR. IN ADDITION...RAOB FROM THE
LESSER ANTILLES SHOW A STRONG MID-LEVEL CIRCULATION ASSOCIATED WITH
ERIKA THAT HAS BEEN LEFT BEHIND OVER THE NORTHERN LEEWARD ISLANDS.
BY TRACING THE CIRRUS CLOUDS ON SATELLITE...ONE CAN CLEARLY SEE
THAT THE SYSTEM IS APPROACHING AN AREA OF EVEN STRONGER
SOUTHWESTERLY UPPER-LEVEL WINDS. THESE WINDS WILL KEEP THE SYSTEM
DECOUPLED AND WILL LIKELY REMOVE ALL THE ADDITIONAL CONVECTION THAT
COULD REDEVELOP.  BECAUSE THE CIRCULATION HAS BECOME LESS
DEFINED...CONVECTION IS NOT ORGANIZED...SURFACE PRESSURES ARE
RISING AND THE WINDS HAVE DECREASED...ERIKA IS NOW CLASSIFIED AS A
REMNANT LOW...AND COULD DEGENERATE EVEN FURTHER INTO A TROUGH OF
LOW PRESSURE ON FRIDAY. THIS WILL BE THE LAST ADVISORY ON ERIKA
UNLESS REGENERATION OCCUR.
 
THE REMANT LOW IS MOVING TOWARD THE WEST OR 280 DEGREES AT 6 KNOTS
AND THIS GENERAL MOTION SHOULD CONTINUE ON FRIDAY WITH A GRADUAL
TURN TO THE NORTHWEST.  THE REMNANTS OF ERIKA COULD STILL PRODUCE
HEAVY RAINS OVER PORTIONS OF THE LESSER ANTILLES AND PUERTO RICO
DURING THE NEXT DAY OR SO.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      04/0300Z 16.8N  65.6W    25 KT...REMNANT LOW
 12HR VT     04/1200Z 17.0N  66.5W    25 KT...REMNANT LOW
 24HR VT     05/0000Z 18.0N  67.5W    20 KT...REMNANT LOW
 36HR VT     05/1200Z 19.5N  68.5W    20 KT...REMNANT LOW
 48HR VT     06/0000Z 21.0N  70.0W    20 KT...REMNANT LOW
 72HR VT     07/0000Z...DISSIPATED
 
$$
FORECASTER AVILA
 

