TROPICAL STORM TOMAS DISCUSSION NUMBER 28

By: National Hurricane Center
By: National Hurricane Center

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TROPICAL STORM TOMAS DISCUSSION NUMBER 28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL212010
1100 PM EDT THU NOV 04 2010

THERE HAS BEEN A SHARP INCREASE IN THE INNER-CORE WIND STRUCTURE AND
CONVECTIVE ORGANIZATION OF TOMAS DURING THE PAST 6 HOURS. ALTHOUGH
BOTH AIR FORCE RESERVE AND NOAA HURRICANE AIRCRAFT INDICATE THERE
IS ABOUT 12 NMI NORTHEASTWARD TILT TO THE VORTEX...THIS HAS NOT
PREVENTED THE CENTRAL PRESSURE FROM FALLING AND THE WINDS FROM
INCREASING. THE MAXIMUM 850-MB FLIGHT-LEVEL WINDS REPORTED BY THE
AIR FORCE WAS 61 KT...AND 58 KT WAS REPORTED AT 700 MB BY THE NOAA
HURRICANE HUNTERS. MAXIMUM SFMR WINDS HAVE BEEN AROUND 56-58 KT.
THE LATEST NOAA RECON PRESSURE WAS DOWN TO 989 MB...AND THAT WAS
WITH 13 KT OF WIND AT THE SURFACE. A COMBINATION OF THESE DATA
EASILY SUPPORT INCREASING THE INTENSITY TO 55 KT...WHICH COULD BE A
LITTLE CONSERVATIVE GIVEN THAT A WARM SPOT HAS APPEARED
INTERMITTENTLY WITHIN A RING OF VERY COLD TOPS OF -80C TO -85C NEAR
THE CENTER.

THE INITIAL MOTION ESTIMATE IS NOW 030/08. TOMAS HAS NOW MOVED NORTH
OF A MID-LEVEL RIDGE THAT LIES EAST-WEST ACROSS THE CENTRAL
CARIBBEAN SEA. TOMAS SHOULD CONTINUE TO MOVE AROUND THE WESTERN
PERIPHERY OF THE RIDGE AND GRADUALLY ACCELERATE NORTHEASTWARD AS IT
COMES UNDER THE INFLUENCE OF MODERATE SOUTHWESTERLY FLOW AHEAD OF A
DEEP MID-LATITUDE TROUGH CURRENTLY MOVING EASTWARD ACROSS THE
EASTERN U.S....FLORIDA...AND THE EASTERN GULF OF MEXICO. THE TRACK
MODELS REMAIN IN EXCELLENT AGREEMENT ON THIS DEVELOPING SCENARIO
THROUGH 48 HOURS...AND THE MODEL TRACKS HAVE EVEN SHIFTED MORE TO
THE EAST ON THE LATEST FORECAST CYCLE. HOWEVER...AFTER THAT TIME...
HOWLING WESTERLY WIND SHEAR IN EXCESS OF 60 KT IS EXPECTED TO SHEAR
APART TOMAS AND LEAVE BEHIND A REMNANT LOW PRESSURE SYSTEM THAT
SHOULD BE STEERED SLOWLY EASTWARD BY WEAKER LOW-LEVEL WESTERLY FLOW
ON THE SOUTH SIDE OF AN EXTRATROPICAL LOW PRESSURE SYSTEM. THE GFDL
AND HWRF MODELS TAKE TOMAS OR ITS REMNANTS RAPIDLY NORTHWARD AND
MERGE IT WITH A DEEP EXTRATROPICAL LOW NEAR THE NORTHEAST U.S.
COAST AND THE CANADIAN MARITIMES. HOWEVER...THE GFS...ECMWF...
UKMET...AND NOGAPS MODELS SHOW TOMAS SHEARING APART AND REMAINING
JUST NORTH OF THE GREATER ANTILLES. THE LATTER SCENARIO IS
PREFERRED GIVEN THE EXTREMELY HOSTILE SHEAR CONDITIONS THAT ARE
FORECAST TO AFFECT THE CYCLONE BY 72 HOURS AND BEYOND. THE OFFICIAL
FORECAST TRACK HAS BEEN SHIFTED A LITTLE TO THE RIGHT OF THE
PREVIOUS TRACK...BUT MAINLY TO ACCOUNT FOR THE MORE EASTERLY
INITIAL POSITION.

TOMAS HAS ABOUT 24 HOURS OR SO TO STRENGTHEN OVER 29C SSTS AND IN A
RELATIVELY LOW SHEAR ENVIRONMENT. HOWEVER...BY 36 HOURS...MID-LEVEL
HUMIDITIES ARE FORECAST TO DECREASE BELOW 40 PERCENT...WHICH COULD
ACT TO ERODE THE INNER-CORE CONVECTION. AS MENTIONED ABOVE...BY 48
HOURS THE VERTICAL SHEAR IS EXPECTED TO INCREASE SHARPLY AND TOMAS
SHOULD BEGIN A STEADY WEAKENING TREND. THE OFFICIAL INTENSITY
FORECAST IS SIMILAR TO BUT SLIGHTLY LOWER THAN THE SHIPS...LGEM...
AND GFDL MODELS.

REGARDLESS OF THE EXACT TRACK AND INTENSITY OF TOMAS...THE MOST
SIGNIFICANT THREAT FROM THIS TROPICAL CYCLONE WILL BE HEAVY
RAINFALL...WHICH COULD PRODUCE FLASH FLOODING AND LIFE-THREATENING
MUD SLIDES OVER HAITI AND THE DOMINICAN REPUBLIC DURING THE NEXT
COUPLE OF DAYS.

FORECAST POSITIONS AND MAX WINDS

INITIAL 05/0300Z 17.3N 75.5W 55 KT
12HR VT 05/1200Z 18.8N 74.6W 65 KT
24HR VT 06/0000Z 21.0N 73.1W 70 KT
36HR VT 06/1200Z 23.4N 71.5W 70 KT
48HR VT 07/0000Z 25.1N 70.2W 55 KT
72HR VT 08/0000Z 27.2N 67.9W 40 KT
96HR VT 09/0000Z 28.3N 65.8W 30 KT...POST-TROPICAL
120HR VT 10/0000Z 28.5N 64.0W 30 KT...POST-TROP/REMNT LOW

$$
FORECASTER STEWART

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