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Hurricane ISABEL


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HURRICANE ISABEL DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT MON SEP 08 2003
 
ISABEL HAS CONTINUED TO RAPIDLY INTENSIFY. THE INITIAL INTENSITY IS
INCREASED TO 100 KT BASED ON SATELLITE INTENSITY ESTIMATES OF 115
KT FROM TAFB AND AFWA...102 KT FROM SAB...AND 102 KT/T5.5 3-HOUR
OBJECTIVE DVORAK INTENSITY ESTIMATES. THE 100 KT INITIAL INTENSITY
IS ALSO CONSISTENT WITH THE LATEST AMSU INTENSITY ESTIMATES OF 100
KT AND 960 MB. OUTFLOW REMAINS QUITE IMPRESSIVE AND CONTINUES TO
IMPROVE AND THE EYE DIAMETER HAS DECREASED DOWN TO 25 NMI.
 
THE INITIAL MOTION ESTIMATE IS 290/12. IS APPEARS THAT ISABEL MAY BE
MAKING THE MORE WESTWARD TURN THAT THE GLOBAL MODELS HAVE BEEN
INDICATING. THE NHC MODEL GUIDANCE IS EVEN MORE TIGHTLY PACKED AND
IN GOOD AGREEMENT ON ISABEL MOVING WEST-NORTHWESTWARD FOR THE NEXT
36 HOURS...AND THEN TURNING MORE WESTWARD AFTER THAT. THIS IS QUITE
REASONABLE GIVEN THE STRENGTH AND EAST-WEST ORIENTATION OF THE
SUBTROPICAL RIDGE LOCATED ALONG 32N LATITUDE. A DISCONCERTING PART
OF THE MODEL GUIDANCE IS THE GFS AND NOGAPS MODELS CONTINUING TO
INSIST THAT ISABEL WILL MAKE A DIP SOUTH-OF-WEST AFTER 72 HOURS.
THEY BRING ISABEL DANGEROUSLY CLOSE TO THE NORTHERN LEEWARD ISLANDS
BY 120 HOURS. THE GFS AND NOGAPS HAD A LEFT OF TRACK BIAS WITH
FABIAN LAST WEEK...SO I PREFER TO WAIT ANOTHER 24 HOURS OR SO TO
SEE IF THIS SAME BIAS DEVELOPS. HOWEVER...THIS SCENARIO CAN NOT BE
COMPLETELY RULED OUT GIVEN THE DEEP MID-/UPPER-LEVEL TROUGH
NORTHWEST OF AFRICA THAT HAS BEEN DIGGING SOUTHWESTWARD. THAT COULD
CREATE ENOUGH LOW-LEVEL RIDGING FROM THE NORTHEAST TO NUDGE ISABEL
A LITTLE SOUTH OF DUE WEST...SIMILAR TO THE GFS-NOGAPS SCENARIO.
 
ISABEL IS ABOUT 18-24 HOURS INTO A RAPID INTENSIFICATION CYCLE...SO
THIS TREND IS FORECAST TO CONTINUE FOR ANOTHER 12 HOURS OR SO.
AFTER REACHING CATEGORY 4 INTENSITY...INNER-CORE CONVECTION AND
EYEWALL DYNAMICS WILL DICTATE ANY INTENSITY CHANGES. HOWEVER...THE
INTENSITY FORECAST COULD EASILY BE TOO LOW GIVEN THE CURRENT AND
FORECAST OUTFLOW PATTERN THAT WILL EVOLVE OVER THE NEXT 48 HOURS.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      08/1500Z 17.2N  42.6W   100 KT
 12HR VT     09/0000Z 17.9N  44.4W   115 KT
 24HR VT     09/1200Z 18.6N  46.8W   120 KT
 36HR VT     10/0000Z 19.2N  49.1W   120 KT
 48HR VT     10/1200Z 19.4N  51.1W   120 KT
 72HR VT     11/1200Z 19.5N  55.0W   120 KT
 96HR VT     12/1200Z 19.5N  58.5W   120 KT
120HR VT     13/1200Z 20.0N  62.5W   120 KT
 
 
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