Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER  16
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT TUE SEP 09 2003
 
THERE HAS BEEN SOME EROSION OF THE EYEWALL CONVECTION IN THE EASTERN
SEMICIRCLE AND THE EYE HAS BECOME LESS DISTINCT OVER THE PAST FEW
HOURS. WATER VAPOR IMAGERY ALSO INDICATES THAT THE OUTFLOW TO THE
NORTHEAST OF ISABEL IS BECOMING SLIGHTLY RESTRICTED.  DVORAK T
NUMBERS ARE 5.5 FROM TAFB AND SAB...AND THE 3-HR AVERAGE RAW ODT IS
ALSO DOWN TO 5.4. THE INITIAL INTENSITY WILL BE HELD AT 115 KT FOR
THIS ADVISORY.  
 
THE INITIAL MOTION ESTIMATE...BASED ON THE LAST 12 HOURS...IS
295/12...ALTHOUGH OVER THE PAST THREE HOURS THE MOTION HAS BEEN
TOWARD THE WEST. THIS IS QUITE POSSIBLY THE BEGINNING OF THE
EXPECTED WESTWARD TURN...BUT THREE HOURS OF MOTION IS NOT ENOUGH TO
BE SURE...ESPECIALLY GIVEN THE DEGRADATION OF THE EYE OBSERVED
DURING THIS PERIOD.  REGARDLESS...ISABEL IS SOUTH OF A MID-LEVEL
RIDGE OF HIGH PRESSURE THAT SHOULD FORCE THE HURRICANE ON A
GENERALLY WESTWARD TRACK OVER THE NEXT THREE DAYS. AFTER THAT...
GLOBAL MODELS GENERALLY SHOW A BREAK IN THE RIDGE BETWEEN 75 AND
80W THAT WOULD ALLOW A TURN BACK TO THE WEST-NORTHWEST ON DAYS 4
AND 5 OF THE FORECAST.  

FOR THE LAST COUPLE OF DAYS...THE GUIDANCE ENVELOPE HAS BEEN
CONSISTENTLY DEFINED BY THE UKMET ON THE NORTH AND THE GFS/NOGAPS
ON THE SOUTH. AMONG THE GLOBAL MODELS...THE UKMET HAS BEEN THE BEST
PERFORMER SO FAR WITH ISABEL AND THE GFS HAS BEEN THE WORST.  THE
UKMET ALSO WAS THE BEST OF THE GLOBAL MODELS FOR FABIAN.  THE
INITIAL VORTEX FOR ISABEL IN THE GFS HAS BEEN CONSISTENTLY MUCH
WEAKER THAN THE INITIALIZATION IN THE UKMET...ALTHOUGH I AM NOT
CERTAIN THAT THIS EXPLAINS THE DIFFERENCES BETWEEN THE TWO MODELS. 
GIVEN THE RECENT MOTION...I HAVE NUDGED THE OFFICIAL FORECAST TRACK
A LITTLE SOUTH OF THE PREVIOUS ADVISORY.  THE NEW TRACK IS IN BEST
AGREEMENT WITH THE GFDL...AND SLIGHTLY ON THE UKMET SIDE OF THE
GLOBAL MODEL CONSENSUS.

ENVIRONMENTAL CONDITIONS SHOULD BE GENERALLY FAVORABLE FOR THE NEXT
SEVERAL DAYS...SO LITTLE OVERALL CHANGE IN STRENGTH IS FORECAST. 
HOWEVER...FLUCTUATIONS IN INTENSITY ARE COMMON IN MAJOR HURRICANES
AND THESE ARE GENERALLY VERY DIFFICULT TO FORECAST.
 
FORECASTER FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      10/0300Z 20.6N  48.8W   115 KT
 12HR VT     10/1200Z 21.3N  50.4W   115 KT
 24HR VT     11/0000Z 21.5N  52.3W   115 KT
 36HR VT     11/1200Z 21.5N  53.9W   115 KT
 48HR VT     12/0000Z 21.5N  55.5W   115 KT
 72HR VT     13/0000Z 21.5N  58.5W   115 KT
 96HR VT     14/0000Z 22.0N  61.5W   110 KT
120HR VT     15/0000Z 23.0N  65.0W   110 KT
 
 
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