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Hurricane ISABEL


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HURRICANE ISABEL DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT WED SEP 10 2003
 
SATELLITE IMAGES SHOW A DISTINCT EYE SURROUNDED BY DEEP CONVECTION.
THE OUTFLOW TO THE WEST AND SOUTH IS IMPRESSIVE BUT IS SOMEWHAT
LIMITED TO THE EAST. SUBJECTIVE T-NUMBERS ARE 6.0 AND 5.5 FROM TAFB
AND SAB..RESPECTIVELY. THE LATEST OBJECTIVE T-NUMBERS ARE BACK UP
TO 6.0 ON THE DVORAK SCALE. INITIAL INTENSITY REMAINS AT 115 KNOTS.
THERE IS NO SHEAR AND THE OCEAN IS INCREASINGLY WARMER. THESE
ENVIRONMENTAL CONDITIONS SHOULD ALLOW SOME ADDITIONAL
STRENGTHENING. BUT...IN MAJOR HURRICANES...CHANGES IN INTENSITY ARE
CONTROLLED IN GENERAL BY EYEWALL THERMODYNAMICS. THEREFORE...SOME
FLUCTUATIONS IN INTENSITY ARE INDICATED TO REFLECT UNCERTAINTIES.
 
THE FORECAST TRACK IS BECOMING RATHER INTERESTING. LAST FEW
SATELLITE IMAGES SUGGEST THAT ISABEL HAS BEGUN TO TURN TOWARD THE
WEST. THE INITIAL MOTION IS NOW ESTIMATED AT 275 DEGREES AT 12
KNOTS. HOWEVER...A LONGER TERM AVERAGE IS STILL TOWARD THE
WEST-NORTHWEST. GLOBAL MODELS CONTINUE TO SHOW THE DEVELOPMENT OF A
STRONG SUBTROPICAL RIDGE NORTH OF ISABEL. DEPENDING UPON THE
FORECAST STRENGTH OF THE RIDGE...EACH MODEL MOVES ISABEL EITHER
WEST OR WEST-NORTHWEST. THE GFS HAS THE STRONGEST RIDGE AND IS
PRODUCING THE SOUTHERMOST AND DANGEROUS TRACK. THE UK HAS A WEAKER
RIDGE WITH THE NORTHERMOST TRACK BUT STILL INDICATING A
WEST-NORTHWEST TO WEST MOTION.  THE OFFICIAL FORECAST IS IN BETWEEN
THESE TWO SOLUTIONS. THE NOGAPS APPEARS TO BE VERY SLOW BUT IT IS
SHOWING THE SAME WEST TO WEST-NORTHWEST TREND. THE BOTTOM LINE IS
THAT A RIDGE IS FORECAST TO DEVELOP BETWEEN THE U.S. EAST COAST AND
BERMUDA. THIS PATTERN WOULD MAINTAIN ISABEL ON A GENERAL WEST TO
WEST-NORTHWEST TRACK FOR THE NEXT SEVERAL DAYS...KEEPING THE CORE
OF THE HURRICANE AWAY FROM THE NORTHERN LEEWARD ISLANDS.

IF THE CURRENT WESTWARD TREND CONTINUES...THE OFFICIAL FORECAST WILL
HAVE TO BE ADJUSTED SLIGHTLY SOUTHWARD IN THE NEXT TERM.
 
FORECASTER AVILA
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      10/0900Z 20.9N  50.2W   115 KT
 12HR VT     10/1800Z 21.5N  52.1W   115 KT
 24HR VT     11/0600Z 21.5N  54.2W   115 KT
 36HR VT     11/1800Z 21.5N  56.0W   115 KT
 48HR VT     12/0600Z 21.5N  58.0W   115 KT
 72HR VT     13/0600Z 21.5N  60.5W   115 KT
 96HR VT     14/0600Z 22.0N  63.5W   110 KT
120HR VT     15/0600Z 23.0N  67.0W   110 KT
 
 
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