Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER  20
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT WED SEP 10 2003
 
SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS T6.5...127 KT...AND SO
THE ADVISORY INTENSITY IS INCREASED TO 125 KT. THE MOST RECENT 3-HR
AVERAGE OBJECTIVE DVORAK INTENSITY ESTIMATE WAS JUST BELOW 130 KT.
ALTHOUGH THERE IS CURRENTLY NO UPPER-LEVEL OUTFLOW TO THE NORTH...
THERE ARE TWO VERY EFFICIENT OUTFLOW CHANNELS OPERATING TO THE WEST
AND EAST OF THE HURRICANE.  ISABEL IS EXPECTED TO REMAIN A MAJOR
HURRICANE THROUGHOUT THE FORECAST PERIOD.  WIND RADII HAVE BEEN
ADJUSTED SLIGHTLY INWARD BASED ON A RECENT QUIKSCAT PASS.
 
THE INITIAL MOTION ESTIMATE IS 270/9.  THE WESTWARD TRACK IS THE
RESULT OF A MID TO UPPER-LEVEL HIGH CURRENTLY LOCATED NORTH OF
ISABEL NEAR 30N.  THIS HIGH IS FORECAST BY GLOBAL MODELS TO SLIDE
WESTWARD WITH ISABEL FOR THE NEXT TWO TO THREE DAYS...AND MAINTAIN
ISABEL ON A TRACK JUST A BIT NORTH OF DUE WESTWARD.  BY DAYS 4 AND
5 OF THE FORECAST PERIOD...NEARLY ALL OF THE GLOBAL MODEL GUIDANCE
SLOWS THE WESTWARD PROGRESSION OF THE HIGH AND ALLOWS THE TRACK TO
SLOW AND BEND SLIGHTLY TO THE RIGHT.  THE FOUR MAIN TRACK MODELS...
THE GFDL...GFS...UKMET...AND NOGAPS...ARE NOW IN VERY GOOD
AGREEMENT THROUGH DAY 5...AS THE GFS HAS SHIFTED SUBSTANTIALLY
NORTHWARD FROM ITS PREVIOUS RUN.  THE OFFICIAL FORECAST HAS BEEN
ADJUSTED NORTHWARD TO BE IN BETTER AGREEMENT WITH THE CURRENT
GUIDANCE...BUT IS STILL ON THE SOUTH EDGE OF THE GUIDANCE ENVELOPE. 
THE ONE OUTLIER IS THE ECMWF...A MODEL VERY SKILLED AT FORECASTING
LARGE-SCALE ATMOSPHERIC PATTERNS...WHICH IS SUBSTANTIALLY SOUTH OF
THE OTHERS IN BRINGING ISABEL NEAR THE EXTREME SOUTHEASTERN BAHAMAS
BY DAY 5. 

IT IS NATURAL TO WANT TO SPECULATE ON THE FORECAST TRACK BEYOND 5
DAYS...BUT IT SIMPLY IS NOT POSSIBLE TO DO SO WITH CONFIDENCE.  THE
GLOBAL MODELS BEGIN TO DIVERGE MARKEDLY ON HOW MUCH RIDGING WILL
REMAIN OFF THE U.S. SOUTHEAST COAST BY DAY 5.  THE EXTENT AND
ORIENTATION OF THIS RIDGING WILL BE CRUCIAL IN DETERMINING THE
POTENTIAL IMPACTS TO THE BAHAMAS AND THE EASTERN UNITED STATES. 
GIVEN THAT ISABEL IS STILL SEVERAL DAYS AWAY FROM THESE
AREAS...THIS WOULD BE A GOOD TIME FOR RESIDENTS TO REVIEW THEIR
PREPAREDNESS PLANS IN CASE ISABEL BECOMES A DIRECT THREAT. 

THE FIRST RECONNAISSANCE AIRCRAFT FLIGHT INTO ISABEL IS SCHEDULED
FOR FRIDAY AFTERNOON.  MISSIONS TO SAMPLE THE SYNOPTIC ENVIRONMENT
OF ISABEL ARE ALSO SCHEDULED TO BEGIN ON FRIDAY. 
 
FORECASTER FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      11/0300Z 21.1N  52.8W   125 KT
 12HR VT     11/1200Z 21.2N  54.3W   125 KT
 24HR VT     12/0000Z 21.4N  56.2W   125 KT
 36HR VT     12/1200Z 21.7N  58.0W   120 KT
 48HR VT     13/0000Z 22.0N  60.0W   120 KT
 72HR VT     14/0000Z 23.0N  64.0W   115 KT
 96HR VT     15/0000Z 24.0N  68.0W   115 KT
120HR VT     16/0000Z 25.0N  71.5W   115 KT
 
 
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