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Hurricane ISABEL


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HURRICANE ISABEL DISCUSSION NUMBER  12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT MON SEP 08 2003
 
DVORAK INTENSITY CLASSIFICATIONS FROM TAFB AND SAB WERE T6.0 OR 115
KT...AND THAT WILL BE THE ADVISORY INTENSITY.  ISABEL HAS AN
IMPRESSIVE OUTFLOW PATTERN ALTHOUGH IT IS BEING SQUEEZED A LITTLE
BIT IN THE SOUTHWEST QUADRANT BY THE UPPER-LEVEL LOW TO ITS WEST.

THE INITIAL MOTION ESTIMATE IS 300/11.  THERE IS A SPLIT IN THE
MODEL GUIDANCE THAT HAS SOME BEARING ON THE POTENTIAL THREAT TO THE
NORTHERN LEEWARD ISLANDS.  WHILE THE CANADIAN AND UKMET MODELS BEND
THE TRACK ONLY SLIGHTLY TO THE LEFT FROM 24-72 HOURS...THE GFS AND
NOGAPS TURN THE TRACK HARDER...TO THE WEST-SOUTHWEST OR EVEN
SOUTHWEST...WHICH BRINGS THE CENTER UNCOMFORTABLY CLOSE TO THESE
ISLANDS.  ONE DIFFERENCE IN THESE MODEL SOLUTIONS IS HOW STRONGLY
ISABEL INTERACTS WITH THE MID TO UPPER-LEVEL LOW CURRENTLY
APPROACHING THE HURRICANE FROM THE NORTHEAST...AS WELL AS THE
MID-LEVEL VORTEX ASSOCIATED WITH TROPICAL DEPRESSION FOURTEEN.  IN
THE UKMET AND CANADIAN MODELS THERE IS NO APPRECIABLE
INTERACTION...WHILE IN THE GFS AND NOGAPS THE LOW IS CLOSE ENOUGH
TO DRAG ISABEL SOUTHWARD.  IN PART BECAUSE OF THE IMPRESSIVE
ANTICYCLONIC OUTFLOW IN THE NORTHEAST QUADRANT OF ISABEL...AND THE
CURRENT DISARRAY OF TD FOURTEEN...MY FEELING IS THAT THE
INTERACTION IS BEING OVERDONE BY THE GFS AND NOGAPS.  THE OFFICIAL
FORECAST IS VERY CLOSE TO THE GLOBAL MODEL CONSENSUS AND GFDL
SOLUTIONS...AND SLIGHTLY TO THE RIGHT OF THE PREVIOUS FORECAST.

I HAVE BACKED OFF A BIT FROM THE INTENSITY FORECAST OF THE PREVIOUS
ADVISORY.  SST ANALYSES SHOW THAT ISABEL WILL BE PASSING OVER THE
COOL WAKE OF FABIAN IN ABOUT 36 HOURS...AND THERE COULD BE SOME
RESTRICTION OF THE OUTFLOW BY THE UPPER LOW APPROACHING FROM THE
NORTHEAST...EVEN IF THAT LOW DOES NOT COME CLOSE ENOUGH TO
APPRECIABLY AFFECT THE TRACK.  IT IS ALSO QUITE RARE FOR STORMS TO
MAINTAIN MAJOR HURRICANE STATUS FOR FIVE DAYS.  EVEN WITH THIS
ADJUSTMENT...THE OFFICIAL FORECAST REMAINS ABOVE THE GFDL AND SHIPS
INTENSITY GUIDANCE.
 
FORECASTER FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/0300Z 18.5N  44.5W   115 KT
 12HR VT     09/1200Z 19.2N  46.2W   120 KT
 24HR VT     10/0000Z 19.9N  48.5W   125 KT
 36HR VT     10/1200Z 20.0N  50.6W   120 KT
 48HR VT     11/0000Z 20.0N  52.5W   115 KT
 72HR VT     12/0000Z 20.0N  56.0W   110 KT
 96HR VT     13/0000Z 20.0N  59.5W   110 KT
120HR VT     14/0000Z 21.0N  63.0W   110 KT
 
 
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