Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER  11
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT MON SEP 08 2003
 
ISABEL HAS CONTINUED ITS RAPID INTENSIFICATION TREND. THE INITIAL
INTENSITY IS INCREASED TO 110 KT BASED ON SATELLITE INTENSITY
ESTIMATES OF 115 KT FROM TAFB AND AFWA...102 KT FROM SAB...AND 113
KT/T5.9 3-HOUR OBJECTIVE DVORAK INTENSITY ESTIMATES.  THE OUTFLOW
REMAINS VERY IMPRESSIVE AND THE OVERALL CONVECTIVE PATTERN HAS ALSO
CONTINUED TO IMPROVE.
 
THE INITIAL MOTION ESTIMATE IS 295/12. THERE HAS BEEN SOME WOBBLING
ALONG THE TRACK THE PAST 6 HOURS...WHICH IS TYPICAL OF INTENSE
HURRICANES. THE NHC MODEL GUIDANCE REMAINS IN GOOD AGREEMENT ON
ISABEL MOVING WEST-NORTHWESTWARD FOR THE NEXT 36 HOURS OR SO...AND
THEN TURNING MORE WESTWARD AFTER THAT. HOWEVER...THE GFS AND NOGAPS
MODELS MAINTAIN A WEST-SOUTHWESTWARD MOTION AFTER 48-72 HOURS. THE
REASON FOR THIS MORE SOUTHERLY TRACK IS NOT APPARENT IN THE MODEL
FIELDS...SO I AM CONTINUING TO PLACE LESS WEIGHT ON THAT SCENARIO
AT THIS TIME BASED ON THOSE MODELS HAVING A PREVIOUS LEFT-BIAS WITH
FABIAN. THE OFFICIAL FORECAST TRACK IS NUDGED SLIGHTLY NORTH OF THE
PREVIOUS TRACK THROUGH 36 HOURS...AND THEN COMES BACK ON TRACK
AFTER THAT. THIS IS CONSISTENT WITH THE GLOBAL MODEL CONSENSUS.

ISABEL IS 24 HOURS INTO A RAPID INTENSIFICATION CYCLE...BUT RARELY
DUE SUCH TRENDS OCCUR FOR MORE THAN 30-36 HOURS. THEREFORE...THE
CURRENT INTENSIFICATION TREND IS LEVELED OFF AFTER ABOUT 12 HOURS
OR SO. HOWEVER...UPPER-LEVEL CONDITIONS ARE FORECAST TO REMAIN
QUITE FAVORABLE THROUGHOUT THE FORECAST PERIOD...SO ISABEL COULD
STILL REACH CATEGORY 4 INTENSITY DURING THE NEXT 12 HOURS OR SO.
AFTER THAT...INNER-CORE CONVECTION AND EYEWALL DYNAMICS WILL
DICTATE ANY FURTHER INTENSITY CHANGES. HOWEVER...THE INTENSITY
FORECAST COULD EASILY BE TOO LOW GIVEN THAT THE OUTFLOW PATTERN IS
EXPECTED TO CONTINUE TO IMPROVE...THE VERTICAL SHEAR IS FORECAST TO
REMAIN LESS THAN 10 KT...AND ISABEL WILL BE MOVING OVER 28C AND
WARMER SSTS.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      08/2100Z 17.9N  43.7W   110 KT
 12HR VT     09/0600Z 18.6N  45.6W   120 KT
 24HR VT     09/1800Z 19.2N  47.9W   125 KT
 36HR VT     10/0600Z 19.5N  50.0W   125 KT
 48HR VT     10/1800Z 19.5N  52.0W   125 KT
 72HR VT     11/1800Z 19.5N  55.5W   125 KT
 96HR VT     12/1800Z 19.5N  59.0W   125 KT
120HR VT     13/1800Z 20.0N  63.0W   125 KT
 
 
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