Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER  47
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT WED SEP 17 2003
 
IF FLIGHT-LEVEL OBSERVATIONS WERE ALL WE HAD...ISABEL WOULD BE A
CATEGORY THREE HURRICANE.  THE HURRICANE HUNTER AIRCRAFT THIS
AFTERNOON FOUND A NUMBER OF SPOTS OF WINDS OF 110-120 KT.  THIS
WOULD NORMALLY CORRESPOND TO SURFACE WINDS OF 100-105 KT. 
HOWEVER...NUMEROUS DROPSONDE PROFILES IN THE HIGH WIND REGIONS OF
THE CIRCULATION SHOW A CONSISTENT AND UNUSUALLY STEEP FALL-OFF OF
WIND IN THE BOUNDARY LAYER.  THIS IS CONSISTENT WITH THE MEAGER
CONVECTION IN THE HURRICANE CORE.  BASED ON THESE PROFILES...THE
INITIAL INTENSITY IS SET AT 90 KT.  THE UPPER-LEVEL OUTFLOW PATTERN
HAS BECOME FAVORABLE...AS WAS FORECAST BY THE GLOBAL MODELS...AND
IN FACT THE CIRCULATION ALOFT IS STRENGTHENING.  HOWEVER...
THERMODYANAMIC FACTORS ARE LIMITING THE ABILITY OF ISABEL TO
COMPLETELY RESPOND TO THE FAVORABLE UPPER-LEVEL FORCING.  THE
OFFICIAL FORECAST DOES NOT ANTICIPATE ANY SIGNIFICANT INCREASE IN
STRENGTH PRIOR TO LANDFALL...BUT SHOULD THERE BE A SUBSTANTIAL
INCREASE IN DEEP CONVECTION ISABEL COULD QUICKLY REACH CATEGORY
THREE STATUS.  

ONCE AGAIN...THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE TRACK
FORECAST OR REASONING.  THE LATEST RUN OF THE GFS IS A LITTLE
FASTER AND SLIGHTLY TO THE RIGHT OF THE PREVIOUS RUN...BUT THE
GUIDANCE REMAINS IN EXCELLENT AGREEMENT.  THE INITIAL MOTION IS NOW
330/12 AS ISABEL BEGINS A MODEST ACCELERATION TOWARD THE COAST. 
SOME ADDITIONAL ACCELERATION IS STILL EXPECTED PRIOR TO LANDFALL.  

ISABEL HAS A LARGE CIRCULATION...INCLUDING A LARGE EXTENT OF
DAMAGING WINDS.  THEREFORE...IT IS ESPECIALLY IMPORTANT NOT TO
FOCUS ON THE PRECISE LANDFALL LOCATION...SINCE SIGNIFICANT IMPACTS
WILL BE FELT AT LARGE DISTANCES FROM THE LANDFALL POINT.

FORECASTER FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      17/2100Z 31.1N  73.3W    90 KT
 12HR VT     18/0600Z 32.7N  74.4W    95 KT
 24HR VT     18/1800Z 35.0N  76.6W    95 KT...INLAND
 36HR VT     19/0600Z 37.6N  78.5W    60 KT...INLAND
 48HR VT     19/1800Z 41.5N  79.0W    40 KT...INLAND
 72HR VT     20/1800Z 52.5N  76.0W    30 KT...EXTRATROPICAL
 96HR VT     21/1800Z...ABSORBED BY EXTRATROPICAL LOW
 
 
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