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Hurricane ISABEL (Text)

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HURRICANE ISABEL DISCUSSION NUMBER  24
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT THU SEP 11 2003
 
ISABEL LOOKS LIKE IT IS ABOUT TO BEGIN AN EYEWALL REPLACEMENT CYCLE. 
AN AMSU MICROWAVE PASS AT 1737Z SHOWED THREE-FOURTHS OF AN OUTER
EYEWALL.  AT 2313Z...AN SSMI PASS SHOWED TWO CONCENTRIC
EYEWALLS...WITH SOME EROSION ON THE NORTH SIDE OF THE INNER
EYEWALL.  THIS IS CONSISTENT WITH CONVENTIONAL IR IMAGERY WHICH
ALSO SHOWS CONSIDERABLE WARMING OF THE CONVECTION IN THE NORTH
EYEWALL OVER THE PAST SEVERAL HOURS.  THE RELATIVELY LIGHT WIND EYE
AND MOAT BETWEEN THE TWO EYEWALLS CAN EVEN BE SEEN IN THE RAW
RETURNED SIGNAL FROM THE QUIKSCAT SCATTEROMETER PASS AT 2116Z. 
WHAT THIS MOST LIKELY MEANS IS THAT THE HURRICANE WILL WEAKEN OVER
THE NEXT 12 HOURS OR SO AS THE INNER EYEWALL COLLAPSES...BUT THEN
COULD REINTENSIFY AFTER THAT AS THE OUTER EYEWALL CONTRACTS.  WE DO
NOT NORMALLY TRY TO INCLUDE THESE KINDS OF FLUCTUATIONS IN THE
OFFICIAL INTENSITY FORECAST...BUT BECAUSE THIS REPLACEMENT SEEMS TO
BE UNDERWAY I HAVE TAKEN A SHOT AT IT.  REGARDLESS OF HOW THE CORE
STRUCTURE EVOLVES IN THE NEAR TERM...ISABEL IS EXPECTED TO REMAIN A
MAJOR HURRICANE THROUGHOUT THE FORECAST PERIOD.  RECENT SST
ANALYSES SHOW THAT THE COOL WAKE OF FABIAN IS GRADUALLY DIMINISHING
AND MAY NOT HAVE A SIGNIFICANT EFFECT ON ISABEL.

A SLIGHT WOBBLE TO THE LEFT IS OCCURRING AT THE MOMENT...BUT THE
LONG-TERM MOTION REMAINS 280/8. THERE HAS BEEN NO SIGNIFICANT
CHANGE TO THE SYNOPTIC THINKING...SHORT-RANGE MODEL GUIDANCE...OR
OFFICIAL TRACK FORECAST.  A DEEP-LAYER HIGH PRESSURE AREA TO THE
NORTH OF ISABEL IS LIKELY TO MAINTAIN THE SLOW WESTWARD TO
WEST-NORTHWESTWARD STEERING OVER THE NEXT SEVERAL DAYS.  BEYOND THE
5-DAY FORECAST PERIOD...MODEL GUIDANCE BEGINS TO DIVERGE AS
STEERING CURRENTS WEAKEN.  IT IS STILL TOO EARLY TO SPECULATE WHAT
PORTIONS OF THE U.S. EAST COAST MIGHT BE AFFECTED BY ISABEL. 
 
FORECASTER FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      12/0300Z 21.6N  56.1W   140 KT
 12HR VT     12/1200Z 21.9N  57.5W   130 KT
 24HR VT     13/0000Z 22.3N  59.4W   135 KT
 36HR VT     13/1200Z 22.7N  61.3W   130 KT
 48HR VT     14/0000Z 23.3N  63.2W   125 KT
 72HR VT     15/0000Z 24.5N  66.5W   115 KT
 96HR VT     16/0000Z 25.5N  69.5W   115 KT
120HR VT     17/0000Z 26.5N  72.5W   110 KT
 
 
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