Tropical Storm ISELLE

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TROPICAL STORM ISELLE DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP102008
800 AM PDT THU AUG 14 2008
 
ANOTHER IMPRESSIVE NOCTURNAL BURST OF CONVECTION DEVELOPED
WELL-DEFINED MID- AND LOW-LEVEL CIRCULATION CENTERS AS NOTED IN A
14/0921Z TRMM OVERPASS. HOWEVER...SINCE THAT TIME...THE OVERALL
CONVECTIVE PATTERN HAS DETERIORATED SOMEWHAT DUE TO INCREASING
NORTHEASTERLY SHEAR. THE INITIAL INTENSITY WAS INCREASED TO 45 KT
AT 12Z AND FOR THE ADVISORY TIME BASED ON CONSENSUS T3.0 SATELLITE
ESTIMATES FROM TAFB AND SAB. THIS MAY BE A LITTLE GENEROUS AT THIS
TIME...BUT ISELLE HAS HAD A HISTORY OF REDEVELOPING DEEP CONVECTION
IN THE FACE OF OTHERWISE HOSTILE CONDITIONS. THE CENTER LOCATION IS
BASED ON EXTRAPOLATING THE VORTEX TILT TO THE NORTHEAST NOTED IN
TRMM IMAGERY AND USING THE STORM MOTION FROM THE PREVIOUS ADVISORY.

TROPICAL STORM ISELLE IS EXPECTED TO CONTINUE IN A GENERAL
WEST-NORTHWESTWARD MOTION THROUGH 72 HOURS...AND THEN TURN WESTWARD
AFTER THAT AS A WEAKENING TROPICAL CYCLONE OR REMNANT LOW THAT IS
STEERED BY THE LOW-LEVEL EASTERLIES NORTH OF THE SYSTEM. THE
MAJORITY OF THE NHC MODEL GUIDANCE SUPPORTS THIS SCENARIO...EXCEPT
FOR THE GFDL AND A UKMET MODELS WHICH TAKE THE CYCLONE SLOWLY
NORTH-NORTHWESTWARD. THE OFFICIAL FORECAST TRACK LEANS MORE TOWARD
A WESTWARD MOTION LATE IN THE PERIOD AS ISELLE IS EXPECTED TO COME
UNDER THE INFLUENCE OF A LARGER CYCLONIC GYRE CURRENTLY CENTERED
ABOUT 650 NMI TO ITS WEST-SOUTHWEST. THE OFFICIAL FORECAST TRACK IS
A LITTLE SOUTH OF THE PREVIOUS TRACK AND SIMILAR TO THE NHC MODEL
CONSENSUS.
 
VERTICAL SHEAR IS EXPECTED REMAIN BETWEEN 25 TO 30 KT THROUGH 96
HOURS. THESE UNFAVORABLE UPPER-LEVEL CONDITIONS...COUPLED WITH
DECREASING SEA-SURFACE TEMPERATURES...ARE EXPECTED TO INDUCE
GRADUAL WEAKENING BY 24-36 HOURS...OF NOT SOONER. THE OFFICIAL
INTENSITY FORECAST IS SIMILAR TO BUT SLIGHTLY LESS THAN THE SHIPS
INTENSITY MODEL.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      14/1500Z 17.8N 109.4W    45 KT
 12HR VT     15/0000Z 18.4N 110.5W    45 KT
 24HR VT     15/1200Z 19.1N 111.8W    45 KT
 36HR VT     16/0000Z 19.7N 112.8W    40 KT
 48HR VT     16/1200Z 20.2N 113.9W    40 KT
 72HR VT     17/1200Z 20.8N 115.4W    35 KT
 96HR VT     18/1200Z 21.0N 116.5W    30 KT
120HR VT     19/1200Z 21.0N 118.0W    25 KT
 
$$
FORECASTER STEWART/BEVEN
 
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