Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER  46
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT WED SEP 17 2003
 
ALTHOUGH PEAK FLIGHT-LEVEL WINDS REMAIN BETWEEN 100 AND 105
KT...WHICH WOULD NORMALLY SUPPORT SURFACE WINDS OF ABOUT 95
KT...DROPSONDE OBSERVATIONS INDICATE THAT A LESS THAN TYPICAL
AMOUNT OF THIS WIND IS MAKING IT DOWN TO THE SURFACE LAYER.  THIS
IS CONSISTENT WITH THE RELATIVELY WEAK CONVECTION IN THE INNER CORE
OF ISABEL.  IN ALL LIKELIHOOD THE SURFACE WINDS ARE CLOSER TO 85
KT.  I HAVE KEPT THE ADVISORY WINDS AT 95 KT FOR NOW...SINCE ANY
INCREASE IN CONVECTION WOULD MORE EFFECTIVELY TRANSPORT THE
MOMENTUM ALOFT DOWNWARD...BUT IF THE CONVECTION DOES NOT STRENGTHEN
THE INTENSITY WILL LIKELY BE LOWERED A BIT THIS AFTERNOON.  EITHER
WAY ISABEL IS A CATEGORY TWO HURRICANE.

THE INITIAL MOTION REMAINS 335/8.  THERE HAS BEEN NO SIGNIFICANT
CHANGE IN THE OFFICIAL FORECAST TRACK...ALTHOUGH THE MODEL GUIDANCE
HAS SHIFTED ITS LANDFALL POINT A FEW MILES TO THE WEST.  THE GFDL
ADJUSTMENT WAS THE LARGEST...ABOUT 30 MILES...AND IT IS RATHER
AMAZING THAT THIS IS ABOUT THE BIGGEST ADJUSTMENT WE HAVE SEEN OVER
THE PAST COUPLE OF DAYS.    

WHILE A MORE FAVORABLE UPPER PATTERN IS BEGINNING TO DEVELOP AS
FORECAST BY THE GLOBAL MODELS...THE LOW-LEVEL ENVIRONMENTAL
THERMODYNAMICS AND CURRENT STORM STRUCTURE ARE EXPECTED TO LIMIT
THE ABILITY OF ISABEL TO RESPOND TO THE UPPER FORCING.  LITTLE
CHANGE IN STRENGTH IS EXPECTED PRIOR TO LANDFALL.  HOWEVER...
INTENSITY FORECASTS TEND TO BE LESS CERTAIN THAN TRACK FORECASTS...
AND AN INTENSITY FORECAST ERROR OF ONE SAFFIR-SIMPSON CATEGORY...UP
OR DOWN...WOULD BE ENTIRELY POSSIBLE.
 
FORECASTER FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      17/1500Z 30.0N  72.6W    95 KT
 12HR VT     18/0000Z 31.4N  73.5W    95 KT
 24HR VT     18/1200Z 33.6N  75.4W    95 KT
 36HR VT     19/0000Z 36.0N  77.3W    70 KT...INLAND
 48HR VT     19/1200Z 39.0N  79.0W    50 KT...INLAND
 72HR VT     20/1200Z 49.0N  77.0W    30 KT...EXTRATROPICAL
 96HR VT     21/1200Z 58.0N  70.0W    25 KT...EXTRATROPICAL
120HR VT     22/1200Z...ABSORBED BY EXTRATROPICAL LOW
 
 
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