WTNT44 KNHC 272055
TCDAT4
 
TROPICAL STORM DON DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
400 PM CDT WED JUL 27 2011
 
AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE
TROPICAL WAVE OVER THE SOUTHERN GULF OF MEXICO FOUND A CLOSED
SURFACE CIRCULATION WITH A CENTRAL PRESSURE OF 1001 MB.  THE
MAXIMUM 1000 FT FLIGHT-LEVEL WINDS WERE 45 KT EAST OF THE CENTER...
AND THERE WERE SEVERAL RELIABLE-LOOKING SMFR SURFACE WIND ESTIMATES
OF 35 KT.  BASED ON THIS...THE SYSTEM IS DESIGNATED AS TROPICAL
STORM DON.  THE AIRCRAFT DATA SHOW THAT THE CIRCULATION CENTER IS
ELONGATED...AND IT IS POSSIBLE SOME REFORMATION OF THE CENTER COULD
OCCUR TONIGHT IN RESPONSE TO CONVECTIVE BURSTS.

THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 295/10.  DON IS SOUTH OF
A LOW/MID-LEVEL RIDGE OVER THE NORTHERN GULF OF MEXICO...AND WATER
VAPOR IMAGERY SHOWS UPPER-LEVEL EASTERLY FLOW DEVELOPING TO THE
NORTH AND NORTHEAST OF THE STORM.  THE LARGE-SCALE MODELS FORECAST
THAT WITHIN 24 HR DON WILL BECOME EMBEDDED IN DEEP-LAYER EASTERLY
TO SOUTHEASTERLY FLOW THAT SHOULD PERSIST FOR SEVERAL DAYS.  THIS
EVOLUTION SHOULD STEER THE STORM GENERALLY NORTHWESTWARD.  WHILE
THE MODELS AGREE WITH THIS SCENARIO...THERE IS A SPREAD IN THE
GUIDANCE ON WHERE DON WILL REACH THE NORTHWESTERN GULF COAST.  THE
GFDL AND GFS ARE FARTHEST TO THE RIGHT...CLOSER TO THE HOUSTON/
GALVESTON AREA.  THE UKMET/ECMWF ARE FARTHEST TO THE LEFT...CLOSER
TO THE BROWNSVILLE AREA.  THE FORECAST TRACK LIES BETWEEN THESE
EXTREMES AND IS CLOSE TO THE VARIOUS CONSENSUS MODELS.
 
DON IS OVER THE WARM WATERS OF THE GULF OF MEXICO...AND THE
GLOBAL MODELS FOR THE MOST PART FORECAST LIGHT TO MODERATE
VERTICAL WIND SHEAR OVER THE SYSTEM FOR THE NEXT 72 HR.  DESPITE
THIS...NONE OF THOSE MODELS SUGGEST SIGNIFICANT STRENGTHENING OF
THE STORM...AND NEITHER DOES THE GFDL.  THE SHIPS...LGEM...AND HWRF
MODELS FORECAST THE SYSTEM TO REACH 55-65 KT BEFORE LANDFALL IN
TEXAS...AND THE INTENSITY FORECAST FOLLOWS THAT SCENARIO IN BEST
AGREEMENT WITH THE SHIPS MODEL.  IT SHOULD BE NOTED THAT THE 48 HR
INTENSITY OF 55 KT IS WELL BEFORE LANDFALL...AND DON COULD GET
STRONGER THAN THIS BETWEEN 48-72 HR.
 
WATCHES AND/OR WARNINGS WILL LIKELY BE REQUIRED FOR PORTIONS OF THE
TEXAS COAST TONIGHT OR THURSDAY.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/2100Z 22.2N  87.0W   35 KT  40 MPH
 12H  28/0600Z 23.1N  88.7W   40 KT  45 MPH
 24H  28/1800Z 24.5N  90.9W   45 KT  50 MPH
 36H  29/0600Z 25.8N  92.8W   50 KT  60 MPH
 48H  29/1800Z 27.1N  94.8W   55 KT  65 MPH
 72H  30/1800Z 29.0N  99.5W   35 KT  40 MPH...INLAND
 96H  31/1800Z 31.0N 103.0W   25 KT  30 MPH...INLAND
120H  01/1800Z...DISSIPATED
 
$$
FORECASTER BEVEN
 

WTNT44 KNHC 280231
TCDAT4
 
TROPICAL STORM DON DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
1000 PM CDT WED JUL 27 2011
 
THE CLOUD PATTERN HAS NOT CHANGED SIGNIFICANTLY DURING THE PAST
SEVERAL HOURS WITH THE EXCEPTION OF THE UPPER-LEVEL OUTFLOW THAT IS
EXPANDING IN THE WESTERN PORTION OF THE CYCLONE. DEEP CONVECTION
NEAR THE CENTER HAS DIMINISHED BUT THERE IS A CYCLONICALLY
CURVED CONVECTIVE BAND TO THE SOUTH. T-NUMBERS HAVE NOT CHANGED AND
THE INITIAL INTENSITY IS KEPT AT 35 KNOTS. ANOTHER RECONNAISSANCE
PLANE IS SCHEDULED TO CHECK THE CYCLONE AT DAYBREAK.
 
DON IS MOVING OVER WARM WATERS AND THE SHIPS GUIDANCE AS WELL AS
MOST OF THE GLOBAL MODELS INDICATE THAT THE SHEAR IS LIKELY TO
REMAIN RELATIVELY LOW...ALLOWING FOR SOME INTENSIFICATION.
HOWEVER...NONE OF THE INTENSITY MODELS SHOW SIGNIFICANT
STRENGTHENING. IT SHOULD BE NOTED THAT THE 48-HR OFFICIAL INTENSITY
FORECAST OF 55 KT IS BEFORE LANDFALL...AND DON COULD GAIN SOME
ADDITIONAL STRENGTH AS IT APPROACHES THE COAST.
 
THE CYCLONE IS MOVING TOWARD THE WEST-NORTHWEST OR 300 DEGREES AT
10 KNOTS. THE RIDGE OVER THE SOUTHERN UNITED STATES CONTROLLING THE
CURRENT MOTION OF DON IS EXPECTED TO PERSIST OR EVEN BUILD WESTWARD
A LITTLE. THEREFORE...NO SIGNIFICANT CHANGE IN THE STEERING PATTERN
IS ANTICIPATED...AND DON SHOULD CONTINUE TO MOVE ON THE SAME
GENERAL WEST-NORTHWEST OR NORTHWEST TRACK TOWARD THE TEXAS COAST.
THE TRACK GUIDANCE IS NOT IN QUITE AS GOOD AGREEMENT AS ONE WOULD
LIKE TO SEE...HOWEVER.  SOME MODELS LIKE THE GFDL AND GFDN BRING
THE CYCLONE ON A MORE NORTHWESTERLY TRACK WHILE OTHERS...LIKE THE
ECMWF...INDICATE A MORE WESTERLY MOTION. THE OFFICIAL FORECAST IS
BASICALLY IN THE MIDDLE OF THE TWO OPTIONS.
 
GIVEN THE CURRENT FORECAST TRACK AND UNCERTAINTIES... A TROPICAL
STORM WATCH IS BEING ISSUED FOR A LARGE PORTION OF TEXAS COAST AT
THIS TIME. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/0300Z 22.8N  88.1W   35 KT  40 MPH
 12H  28/1200Z 23.6N  89.5W   40 KT  45 MPH
 24H  29/0000Z 25.0N  91.5W   45 KT  50 MPH
 36H  29/1200Z 26.2N  93.6W   50 KT  60 MPH
 48H  30/0000Z 27.5N  96.0W   55 KT  65 MPH
 72H  31/0000Z 29.5N 100.0W   25 KT  30 MPH...INLAND
 96H  01/0000Z...DISSIPATED
 
$$
FORECASTER AVILA
 

WTNT44 KNHC 280840
TCDAT4
 
TROPICAL STORM DON DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
400 AM CDT THU JUL 28 2011
 
DON HAS NOT CHANGED APPRECIABLY DURING THE PAST SEVERAL HOURS...
MAINTAINING A SMALL AREA OF CONVECTION NEAR THE CENTER.  THERE IS
NOT MUCH ORGANIZATION IN THE INFRARED CLOUD PATTERN...WHICH IS
CONFIRMED BY A TRMM MICROWAVE PASS AT 0608Z. ASCAT DATA FROM 0332Z
SUPPORTED AN INITIAL INTENSITY OF AROUND 35 KT...WITH SATELLITE
CLASSIFICATIONS AT OR BELOW THAT VALUE.  THE ASCAT DATA CONFIRMED
THE EARLIER AIRCRAFT MEASUREMENTS THAT DON IS A RATHER SMALL
TROPICAL CYCLONE.  THE NEXT AIRCRAFT MISSION IS SCHEDULED FOR 1200Z
THIS MORNING.
 
THE INTENSITY FORECAST IS TRICKY.  WHILE THE LARGE-SCALE ENVIRONMENT
DOES NOT APPEAR TO HAVE MUCH SHEAR...THE LOW- AND MID-LEVEL CENTERS
ARE NOT WELL-ALIGNED INITIALLY...WHICH WAS APPARENT ON A 2316Z
SSMIS MICROWAVE IMAGE. THE GFS/ECMWF MODELS HAVE A REASONABLE
REPRESENTATION OF THIS INITIAL STRUCTURE AND KEEP THE CENTERS FROM
VERTICALLY STACKING...POSSIBLY WHY THESE MODELS DO NOT SHOW
MUCH INTENSIFICATION.  WHILE THE STATISTICALLY MODELS STILL
FORECAST STEADY STRENGTHENING...THE HWRF/GFDL MODELS FORECAST A
SLOW DECLINE.  ANOTHER FACTOR TO CONSIDER IS THAT THE SIZE OF DON
MAKES IT SUSCEPTIBLE TO RAPID CHANGES IN STRENGTH...BOTH UP AND
DOWN...THAT ARE NEARLY IMPOSSIBLE TO FORECAST.  GIVEN THE REDUCED
ORGANIZATION...THE NHC INTENSITY FORECAST IS LOWERED SOMEWHAT FROM
THE PREVIOUS FORECAST...BUT IS STILL ON THE UPPER END OF THE
GUIDANCE ENVELOPE NEAR A COMPOSITE OF THE SHIPS/LGEM MODELS.
 
BEST ESTIMATE OF INITIAL MOTION IS 300/9... WITH OVERNIGHT MICROWAVE
IMAGES SUGGESTING THE SMALL CENTER HAS BEEN MOVING ERRATICALLY.  DON
IS MOVING AROUND THE SOUTHERN PERIPHERY OF A RIDGE OVER THE
SOUTHERN UNITED STATES.  THIS RIDGE IS FORECAST TO BUILD SLIGHTLY
DURING THE NEXT DAY OR TWO AS A SERIES OF WEAK IMPULSES MOVE AWAY
FROM THE NORTHERN GULF COAST.  THIS SYNOPTIC PATTERN SHOULD STEER
THE CYCLONE GENERALLY TO THE WEST-NORTHWEST AND ACCELERATE IT.  THE
TRACK GUIDANCE HAS SHIFTED A BIT TO THE WEST OVERNIGHT WITH LESS
SPREAD THAN EARLIER.  THIS SHIFT TO THE LEFT SEEMS REASONABLE WITH
THE BUILDING RIDGE AND THE NHC FORECAST WILL BE MOVED IN THAT
DIRECTION...BUT STILL LIES TO THE RIGHT OF THE MODEL CONSENSUS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/0900Z 23.0N  88.7W   35 KT  40 MPH
 12H  28/1800Z 23.9N  90.3W   40 KT  45 MPH
 24H  29/0600Z 25.1N  92.5W   45 KT  50 MPH
 36H  29/1800Z 26.3N  94.7W   50 KT  60 MPH
 48H  30/0600Z 27.3N  97.1W   50 KT  60 MPH
 72H  31/0600Z 29.0N 101.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  01/0600Z...DISSIPATED
 
$$
FORECASTER BLAKE/BROWN
 

WTNT44 KNHC 281502
TCDAT4
 
TROPICAL STORM DON DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
1000 AM CDT THU JUL 28 2011

THE CENTER OF DON REMAINS PARTLY EXPOSED ON THE NORTH SIDE OF A
PERSISTENT AREA OF CONVECTION THIS MORNING.  AN AIR FORCE RESERVE
HURRICANE HUNTER AIRCRAFT HAS TWICE EXTRAPOLATED A MINIMUM PRESSURE
OF 1001 MB.  THE AIRCRAFT HAS ALSO REPORTED 850 MB FLIGHT-LEVEL
WINDS OF 52 KT AND RELIABLE-LOOKING WINDS OF 35-40 KT FROM THE
SFMR.  BASED ON THIS...THE INITIAL INTENSITY IS INCREASED TO 40 KT.

THE INITIAL MOTION IS NOW 305/12.  DON IS TO THE SOUTH AND SOUTHWEST
OF A DEEP-LAYER RIDGE OVER THE SOUTHEASTERN UNITED STATES...AND THE
LARGE-SCALE MODELS FORECAST THIS FEATURE TO PERSIST FOR THE NEXT
36-48 HR.  THIS SHOULD STEER DON GENERALLY NORTHWESTWARD TO WEST-
NORTHWESTWARD UNTIL LANDFALL ON THE TEXAS COAST BETWEEN 36-48 HR. 
WHILE THE TRACK GUIDANCE AGREES ON THIS SCENARIO...THERE HAS BEEN A
SIGNIFICANT NORTHWARD SHIFT IN THE GUIDANCE SINCE THE PREVIOUS
ADVISORY...WITH THE CENTER OF THE GUIDANCE ENVELOPE NOW NORTH OF
CORPUS CHRISTI.  THE NEW TRACK FORECAST WILL ALSO SHIFT NORTHWARD
BUT STAYS TO THE SOUTH OF THE CENTER OF THE NEW GUIDANCE ENVELOPE. 
IT SHOULD BE NOTED THAT THE ECMWF AND UKMET FORECAST TRACKS ARE ON
THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE TO THE SOUTH OF THE
CURRENT FORECAST TRACK.

ANALYSES FROM THE SHIPS MODEL AND FROM CIMSS AT THE UNIVERSITY OF
WISCONSIN SHOW THAT DON IS EXPERIENCING 10-15 KT OF NORTHERLY
VERTICAL WIND SHEAR.  LIGHT/MODERATE SHEAR IS NOW FORECAST TO
CONTINUE UNTIL THE CYCLONE MAKES LANDFALL.  IN ADDITION...THE
CYCLONE IS ON THE EDGE OF AN AREA OF DRY AIR IN THE WESTERN GULF OF
MEXICO.  THESE FACTORS COULD AT LEAST SLOW INTENSIFICATION...AND
NONE OF THE INTENSITY GUIDANCE CURRENTLY SHOWS DON BECOMING A
HURRICANE BEFORE LANDFALL.  THE NEW INTENSITY FORECAST IS BASICALLY
AN UPDATE OF THE PREVIOUS PACKAGE IN BEST AGREEMENT WITH THE SHIPS
MODEL.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/1500Z 24.1N  90.1W   40 KT  45 MPH
 12H  29/0000Z 24.9N  91.5W   45 KT  50 MPH
 24H  29/1200Z 26.1N  93.8W   50 KT  60 MPH
 36H  30/0000Z 27.3N  96.0W   50 KT  60 MPH
 48H  30/1200Z 28.5N  98.2W   40 KT  45 MPH...INLAND
 72H  31/1200Z 30.0N 102.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  01/1200Z...DISSIPATED
 
$$
FORECASTER BEVEN
 

WTNT44 KNHC 282034
TCDAT4
 
TROPICAL STORM DON DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
400 PM CDT THU JUL 28 2011
 
DON HAS A CLASSIC SHEAR PATTERN IN SATELLITE IMAGERY THIS AFTERNOON
WITH STRONG BURSTS OF CONVECTION OCCURRING NEAR AND SOUTH OF THE
CENTER.  ANALYSES FROM THE SHIPS MODEL AND FROM CIMSS AT THE
UNIVERSITY OF WISCONSIN INDICATE 10-15 KT OF NORTHERLY VERTICAL
WIND SHEAR CONTINUING OVER THE STORM.  IN ADDITION...A STREAM OF
ARC CLOUDS/GUSTS FRONTS ON THE EASTERN SIDE OF THE CIRCULATION
SUGGESTS THAT DRY AIR IS BEING ENTRAINED INTO THE CONVECTION.  DATA
FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT SHOWED THE
CENTRAL PRESSURE RISING TO 1005 MB...WHILE THE AIRCRAFT WINDS
SUPPORTED AN INITIAL INTENSITY OF 40 KT.
 
THE INITIAL MOTION IS NOW 305/14.  DON REMAINS TO THE SOUTH AND
SOUTHWEST OF A DEEP-LAYER RIDGE OVER THE SOUTHEASTERN UNITED
STATES...AND THE LARGE-SCALE MODELS FORECAST THIS FEATURE TO
PERSIST FOR THE NEXT 36-48 HR.  THIS SHOULD STEER DON GENERALLY
NORTHWESTWARD TO WEST-NORTHWESTWARD UNTIL LANDFALL ON THE TEXAS
COAST IN ABOUT 36 HR.  THE TRACK GUIDANCE...WHICH SHIFTED NORTHWARD
BETWEEN 06Z AND 12Z...HAS SHIFTED SOUTHWARD FOR THIS ADVISORY.  THE
NEW FORECAST TRACK HAS BEEN ONLY SLIGHTLY ADJUSTED TO THE SOUTH AND
LIES ON THE RIGHT SIDE OF THE GUIDANCE ENVELOPE.  SOME ADJUSTMENT
TO THE FORECAST TRACK MAY BE NECESSARY IF THE TRACK GUIDANCE
STABILIZES AROUND A TRACK SOUTH OF THE CURRENT FORECAST.
 
THE LARGE-SCALE MODELS AGAIN FORECAST MODERATE SHEAR TO CONTINUE
UNTIL DON MAKES LANDFALL.  THIS AND CONTINUED INTERACTION WITH DRY
AIR OVER THE WESTERN GULF OF MEXICO IS LIKELY TO IMPEDE
INTENSIFICATION...AND THE INTENSITY GUIDANCE IS IN GOOD AGREEMENT
THAT DON WILL MAKE LANDFALL AS A TROPICAL STORM AND NOT AS A
HURRICANE.  THE NEW INTENSITY FORECAST CALLS FOR A LITTLE LESS
STRENGTHENING DURING THE FIRST 12-24 HR DUE TO THE PRESENCE OF
SHEAR AND ARC CLOUDS...THEN CALLS FOR DON TO REACH A PEAK INTENSITY
OF 50 KT NEAR LANDFALL.  AFTER LANDFALL...THE CYCLONE SHOULD WEAKEN
TO A TROPICAL DEPRESSION BY THE 48 HR POINT AND TO A REMNANT LOW BY
THE 72 HR POINT.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/2100Z 24.9N  91.3W   40 KT  45 MPH
 12H  29/0600Z 25.8N  93.1W   40 KT  45 MPH
 24H  29/1800Z 26.8N  95.2W   45 KT  50 MPH
 36H  30/0600Z 27.8N  97.5W   50 KT  60 MPH...INLAND
 48H  30/1800Z 28.8N 100.0W   30 KT  35 MPH...INLAND
 72H  31/1800Z 30.5N 103.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  01/1800Z...DISSIPATED
 
$$
FORECASTER BEVEN
 

WTNT44 KNHC 290232
TCDAT4
 
TROPICAL STORM DON DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
1000 PM CDT THU JUL 28 2011
 
BOTH NOAA AND AIR FORCE RECONNAISSANCE PLANES HAVE BEEN
INVESTIGATING TROPICAL STORM DON AND FOUND THAT THE CYCLONE HAD
JOGGED TO THE WEST DURING THE PAST FEW HOURS AND THAT THE CYCLONE
IS A LITTLE BIT STRONGER. THE MINIMUM CENTRAL PRESSURES REPORTED BY
NOAA AND AIR FORCE PLANE EARLIER THIS EVENING WERE 996 AND 998
RESPECTIVELY. MORE RECENTLY A HIGHER PRESSURE WAS REPORTED BUT THE
DROPSONDE DID NOT HIT THE VERY SMALL CENTER. SATELLITE INTENSITY
ESTIMATES FROM TAFB AND SAB HAVE INCREASED TO 3.0 AND 3.5 ON THE
DVORAK SCALE. THE INITIAL HAS BEEN INCREASED TO 45 KNOTS PRIMARILY
BASED ON A BELIEVABLE 43-KNOT SFMR REPORT. THE CYCLONE HAS BEEN
UNDER THE INFLUENCE OF NORTHERLY SHEAR AND THE LOW-LEVEL CENTER IS
STILL TILTED SOUTHWARD WITH HEIGHT AS REPORTED BY BOTH PLANES.
SINCE NO SIGNIFICANT DECREASE OF THE SHEAR IS ANTICIPATED AND THE
CYCLONE IS INTERACTING WITH DRY AIR OVER THE WESTERN GULF OF
MEXICO...ONLY A SMALL AMOUNT OF STRENGTHENING IS FORECAST BEFORE
LANDFALL. IN FACT NONE OF THE GUIDANCE SUGGEST IMPORTANT CHANGES IN
INTENSITY.    

DURING THE PAST FEW HOURS...DON HAS BEEN MOVING BETWEEN THE WEST AND 
WEST-NORTHWEST AT 12 KNOTS. A STRONG HIGH PRESSURE SYSTEM OVER THE
SOUTHERN UNITED STATES HAS BEEN CONTROLLING THE TRACK OF THE
CYCLONE. SINCE THIS HIGH IS FORECAST BY MOST OF THE GLOBAL MODELS
TO PERSIST...A CONTINUATION OF A GENERALLY WEST-NORTHWESTWARD TRACK 
IS ANTICIPATED UNTIL LANDFALL. THE OFFICIAL TRACK HAS BEEN SHIFTED
SOUTHWARD A LITTLE BIT AND THIS DUE TO THE INITIAL WESTWARD JOG AND
NOT DUE TO ANY IMPORTANT CHANGE IN THE STEERING PATTERN. GIVEN THE
SMALL SOUTHWARD SHIFT OF THE TRACK...THE TROPICAL STORM WATCH FOR
THE SOUTHERN TEXAS COAST HAS BEEN REPLACED WITH A TROPICAL STORM
WARNING. 

INTERESTS IN EXTREME NORTHEAST MEXICO SHOULD CLOSELY MONITOR THE
PROGRESS OF DON. AN UNEXPECTED SMALL DEVIATION TO THE SOUTH OF THE
TRACK COULD NECESSITATE THE ISSUANCE OF WARNINGS FOR THE EXTREME
NORTHEASTERN COAST OF MEXICO.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/0300Z 24.7N  92.5W   45 KT  50 MPH
 12H  29/1200Z 25.5N  94.3W   50 KT  60 MPH
 24H  30/0000Z 26.6N  96.6W   55 KT  65 MPH
 36H  30/1200Z 27.5N  99.0W   30 KT  35 MPH...INLAND
 48H  31/0000Z 28.5N 101.5W   25 KT  30 MPH...INLAND
 72H  01/0000Z...DISSIPATED
 
$$
FORECASTER AVILA
 

WTNT44 KNHC 290839
TCDAT4
 
TROPICAL STORM DON DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
400 AM CDT FRI JUL 29 2011
 
DON CONTINUES TO HAVE A SHEARED APPEARANCE ON SATELLITE IMAGES WITH
THE LOW-LEVEL CENTER DISPLACED NEAR THE NORTHERN EDGE OF AN
ELONGATED AREA OF STRONG CONVECTION.  THIS SHEAR CAN ALSO BE SEEN
IN RECONNAISSANCE DATA...WHICH SHOWED THAT THE SURFACE CENTER IS
DISPLACED SOMEWHAT TO THE NORTH OF THE 850 MB FLIGHT-LEVEL CENTER. 
THE INITIAL INTENSITY REMAINS 45 KT...A BLEND OF THE ESTIMATES FROM
SATELLITE AND AIRCRAFT DATA.
 
MODERATE NORTHERLY SHEAR IS FORECAST UNTIL DON MAKES LANDFALL ALONG
WITH SOME DRY AIR ALOFT.  THIS COMBINATION WILL PROBABLY LIMIT
SIGNIFICANT INTENSIFICATION EVEN THOUGH THE STORM IS MOVING OVER
VERY WARM WATERS.  MOST OF THE GUIDANCE SHOWS JUST A LITTLE MORE
STRENGTHENING...AND THE OFFICIAL INTENSITY FORECAST IS BASICALLY AN
UPDATE OF THE PREVIOUS PACKAGE.  AFTER MOVING THROUGH TEXAS...THIS
SMALL SYSTEM WILL NOT LAST VERY LONG AFTER INTERACTING WITH THE
HIGH TERRAIN OF MEXICO...AND DISSIPATION IS LIKELY BETWEEN 36 AND
48 HOURS.
 
AIRCRAFT FIXES SUGGEST DON IS MOVING ABOUT 295/12.  HIGH PRESSURE
RIDGING OVER THE SOUTHERN UNITED STATES WILL PROBABLY STEER THE
CYCLONE ALONG THAT GENERAL COURSE UNTIL LANDFALL...PERHAPS EVEN A
LITTLE MORE TO THE LEFT AS THE RIDGE BUILDS.  THE GUIDANCE IS IN
GOOD AGREEMENT...ALTHOUGH THE USUALLY RELIABLE ECMWF MODEL IS
FARTHER TO THE NORTHEAST.  AN EXAMINATION OF THE ECMWF FIELDS
INDICATES THAT THE MODEL DECOUPLES THE LOW- AND MID-LEVEL
CENTERS...ALLOWING DON TO MOVE MORE TO THE NORTHWEST.  THIS DOES
NOT SEEM LIKELY AS ENVIRONMENTAL CONDITIONS ARE NOT EXPECTED TO
CHANGE SIGNIFICANTLY FROM NOW UNTIL LANDFALL.  THUS THE NHC
FORECAST WILL STAY CLOSE TO THE DYNAMICAL MODEL CONSENSUS AND THE
PREVIOUS FORECAST.
 
INTERESTS IN EXTREME NORTHEAST MEXICO SHOULD CLOSELY MONITOR THE
PROGRESS OF DON. AN UNEXPECTED SMALL DEVIATION TO THE SOUTH OF THE
FORECAST TRACK COULD NECESSITATE THE ISSUANCE OF WARNINGS FOR THE
EXTREME NORTHEASTERN COAST OF MEXICO.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/0900Z 25.3N  93.6W   45 KT  50 MPH
 12H  29/1800Z 26.1N  95.5W   50 KT  60 MPH
 24H  30/0600Z 27.0N  97.8W   45 KT  50 MPH...INLAND
 36H  30/1800Z 27.8N 100.4W   30 KT  35 MPH...INLAND
 48H  31/0600Z...DISSIPATED
 
$$
FORECASTER BLAKE/STEWART
 

WTNT44 KNHC 291433
TCDAT4
 
TROPICAL STORM DON DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
1000 AM CDT FRI JUL 29 2011
 
SATELLITE IMAGES SHOW THAT DON HAS BECOME A LITTLE BETTER ORGANIZED
THIS MORNING WITH INCREASED CONVECTIVE BANDING AROUND THE CENTRAL
CONVECTION...ESPECIALLY IN THE SOUTHERN SEMICIRCLE.  HOWEVER...THE
STORM CONTINUES TO EXPERIENCE 10-15 KT OF NORTHERLY VERTICAL WIND
SHEAR...WITH AN ELONGATED OVERALL CLOUD PATTERN AND A STREAM OF ARC
CLOUDS IN THE EASTERN AND NORTHEASTERN QUADRANTS OF THE CYCLONE.
AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT HAS REPORTED 850 MB
FLIGHT-LEVEL WINDS OF 51 KT...AND THE CENTRAL PRESSURE ESTIMATED
FROM THE AIRCRAFT DATA IS NEAR 1002 MB.  THE INITIAL INTENSITY
REMAINS 45 KT.
 
THE INITIAL MOTION IS NOW 300/12.  DEEP-LAYER RIDGING OVER THE
SOUTHEASTERN UNITED STATES SHOULD STEER DON GENERALLY
WEST-NORTHWESTWARD UNTIL THE CYCLONE DISSIPATES OVER LAND IN
36-48 HR.  THE NEW FORECAST TRACK HAS CHANGED LITTLE FROM THE
PREVIOUS TRACK AND IS NEAR THE CENTER OF THE TRACK GUIDANCE
ENVELOPE.
 
DON SHOULD CONTINUE TO EXPERIENCE MODERATE SHEAR UNTIL THE CENTER
MAKES LANDFALL IN ABOUT 18 HR.  IN ADDITION...WATER VAPOR IMAGERY
AND MICROWAVE PRECIPITABLE WATER DATA SHOW DRY AIR CLOSE TO THE
WESTERN SIDE OF DON.  THIS COMBINATION SHOULD CONTINUE TO IMPEDE
SIGNIFICANT STRENGTHENING BEFORE LANDFALL...AND THUS THE INTENSITY
FORECAST SHOWS ONLY SLIGHT STRENGTHENING.  DON SHOULD WEAKEN
STEADILY AFTER LANDFALL...AND THE SYSTEM IS EXPECTED TO DISSIPATE
COMPLETELY BY 48 HR IN AGREEMENT WITH THE DYNAMICAL MODEL GUIDANCE.
 
INTERESTS IN EXTREME NORTHEAST MEXICO SHOULD CONTINUE TO CLOSELY
MONITOR THE PROGRESS OF DON. ANY SMALL DEVIATION TO THE SOUTH OF
THE FORECAST TRACK COULD NECESSITATE THE ISSUANCE OF WARNINGS FOR
THE EXTREME NORTHEASTERN COAST OF MEXICO.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/1500Z 26.2N  94.9W   45 KT  50 MPH
 12H  30/0000Z 26.8N  96.7W   50 KT  60 MPH
 24H  30/1200Z 27.7N  99.1W   35 KT  40 MPH...INLAND
 36H  31/0000Z 28.3N 101.6W   25 KT  30 MPH...INLAND
 48H  31/1200Z...DISSIPATED
 
$$
FORECASTER BEVEN
 

WTNT44 KNHC 292036
TCDAT4
 
TROPICAL STORM DON DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
400 PM CDT FRI JUL 29 2011
 
SATELLITE IMAGERY SHOWS THAT DON REMAINS A SHEARED SYSTEM THIS
AFTERNOON...WITH THE LOW-LEVEL CENTER NEAR THE NORTHEASTERN EDGE OF
A DISORGANIZED MASS OF STRONG CONVECTION.  AN AIR FORCE RESERVE
HURRICANE HUNTER PLANE MEASURED 56 KT FLIGHT-LEVEL WINDS AT 850 MB
AND ESTIMATED SURFACE WINDS OF 46 KT WITH THE SFMR...BOTH IN THE
NORTHEASTERN QUADRANT.  BASED ON THIS...THE INITIAL INTENSITY
REMAINS 45 KT.  IT SHOULD BE NOTED THAT DOPPLER WIND DISPLAYS FROM
THE BROWNSVILLE WSR-88D HAVE RECENTLY SHOWN A WELL-DEFINED
MESOCYCLONE IN A STRONG CONVECTIVE CELL WELL TO THE SOUTHWEST OF
THE CENTER AND THE PRIMARY CONVECTION.
 
THE INITIAL MOTION IS 300/14.  DEEP-LAYER RIDGING OVER THE
SOUTHEASTERN UNITED STATES SHOULD STEER DON GENERALLY
WEST-NORTHWESTWARD UNTIL DISSIPATION.  THE FORECAST TRACK CALLS FOR
THE SYSTEM TO MAKE LANDFALL BETWEEN BROWNSVILLE AND CORPUS CHRISTI
IN THE NEXT 12 HR...FOLLOWED BY A MOTION ACROSS SOUTH TEXAS INTO
NORTHEASTERN MEXICO.  THIS FORECAST TRACK IS AN UPDATE OF THE
PREVIOUS TRACK.
 
EVEN THOUGH THE 12 HR FORECAST POINT SHOWS WEAKENING...THERE IS
STILL AN OPPORTUNITY FOR DON TO STRENGTHEN A LITTLE IN THE FEW
HOURS REMAINING BEFORE LANDFALL.  THEREAFTER...THE CYCLONE SHOULD
STEADILY WEAKEN AS IT CROSSES SOUTHERN TEXAS...AND IT IS FORECAST
TO DISSIPATE OVER NORTHEASTERN MEXICO BY 48 HR.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/2100Z 26.9N  96.2W   45 KT  50 MPH
 12H  30/0600Z 27.5N  98.0W   40 KT  45 MPH...INLAND
 24H  30/1800Z 28.2N 100.6W   30 KT  35 MPH...INLAND
 36H  31/0600Z 28.8N 103.3W   20 KT  25 MPH...POST-TROP/REMNT LOW
 48H  31/1800Z...DISSIPATED
 
$$
FORECASTER BEVEN
 

WTNT44 KNHC 300234
TCDAT4
 
TROPICAL DEPRESSION DON DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
1000 PM CDT FRI JUL 29 2011
 
THE CLOUD PATTERN ASSOCIATED WITH DON HAS DETERIORATED SIGNIFICANTLY
DURING THE PAST FEW HOURS AS INDICATED BY RADAR AND SATELLITE. THE 
SIGNIFICANT WEATHER OVER WATER HAS LARGELY DISSIPATED AND MOST OF
THE SHOWER ACTIVITY HAS MOVED INLAND.  DATA FROM AN AIR FORCE
HURRICANE HUNTER PLANE INDICATE THAT THE WINDS ARE ALSO RAPIDLY
DECREASING.  ON THIS BASIS...DON HAS BEEN DOWNGRADED TO A TROPICAL
DEPRESSION AND THE TROPICAL STORM WARNING FOR THE TEXAS COAST HAS
BEEN DISCONTINUED. 

THE DEPRESSION IS MOVING TOWARD THE WEST-NORTHWEST AT 12 KNOTS AND
THE CENTER IS CROSSING THE COAST IN THE VICINITY OF BAFFIN BAY. THE
DEPRESSION SHOULD CONTINUE TO MOVE FARTHER INLAND ON THIS GENERAL
TRACK UNTIL DISSIPATION IN A DAY OR SO. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  30/0300Z 27.2N  97.5W   30 KT  35 MPH
 12H  30/1200Z 28.0N  99.5W   25 KT  30 MPH...INLAND
 24H  31/0000Z 28.5N 102.0W   20 KT  25 MPH...INLAND
 36H  31/1200Z...DISSIPATED
 
$$
FORECASTER AVILA
 

