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Hurricane ISABEL (Text)

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HURRICANE ISABEL DISCUSSION NUMBER  14
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT TUE SEP 09 2003
 
SATELLITE INTENSITY ESTIMATES FROM ALL THREE AGENCIES REMAIN AT 115
KT. THE EYE BECAME CLOUD-COVERED EARLIER THIS MORNING...BUT OVER
THE PAST 3 HOURS THE EYE HAS CLEARED OUT...BECOME BETTER DEFINED
...AND EYEWALL CONVECTIVE CLOUD TOPS HAVE STARTED TO COOL.
THEREFORE...THE INITIAL INTENSITY REMAINS AT 115 KT FOR THIS
ADVISORY...DESPITE THE WEAKENING TREND INDICATED BY THE 3-HOUR
OBJECTIVE T-NUMBERS.

THE INITIAL MOTION ESTIMATE IS 300/12. ISABEL HAS BEEN MAINTAINING A
STEADY WEST-NORTHWESTWARD MOTION FOR THE PAST 48 HOURS...DESPITE
MOST OF THE NHC MODEL GUIDANCE FORECASTING A TURN MORE TOWARD THE
WEST. IT APPEARS THAT ISABEL IS BEING INFLUENCED BY THE SOUTHERLY
FLOW ON THE EAST SIDE OF A LARGE MID-/UPPER-LOW JUST NORTH OF THE
LEEWARD ISLANDS. THIS LOW IS FORECAST BY ALL THE GLOBAL MODELS TO
MOVE QUICKLY NORTHWESTWARD AND WEAKEN DURING THE NEXT 48-72 HOURS.
THE WEAKENING OF THE LOW COMBINED WITH A BUILDING MID-LEVEL RIDGE
NEAR BERMUDA SHOULD ALLOW ISABEL TO MOVE IN A WESTWARD MOTION BY 24
HOURS OR SO. THE GFDL...GFS...AND NOGAPS MODEL CONTINUE TO FORECAST
A SHARP WEST-SOUTHWESTWARD MOTION AFTER 36 HOURS. OUT OF RESPECT
FOR THESE MODELS...A SLIGHT SOUTHWARD JOG IS INDCIATED IN THE
FORECAST TRACK. THE UKMET...HOWEVER...MODEL IS NOT FORECASTING THAT
SOUTHWARD JOG. THE OFFICIAL FORECAST TRACK IS ESSENTIALLY AN UPDATE
OF THE PREVIOUS TRACK AND IS CLOSE TO THE NHC MODEL CONSENSUS.

THE UPPER-LEVEL OUTFLOW PATTERN REMAINS QUITE IMPRESSIVE...
ESPECIALLY WITH THE DEEPENING TROUGH TO THE EAST OF ISABEL
ENHANCING THE OUTFLOW IN THE EASTERN SEMICIRCLE...WHILE THE LARGE
UPPER-LEVEL LOW TO THE WEST IS ENHANCING THE OUTFLOW IN THAT AREA.
THIS FAVORABLE OUTFLOW PATTERN IS FORECAST TO PERSIST FOR AT LEAST
ANOTHER 48 HOURS...SO SOME ADDITIONAL STRENGTHENING IS POSSIBLE.
GIVEN THAT ISABEL IS ALREADY A CAT 4 HURRICANE...SPECIFIC
INTENSIFICATION WILL BE DICTATED BY EYEWALL DYNAMICS LIKE EYEWALL
REPLACEMENT CYCLES THAT CAN NOT BE FORECAST WITH ANY SKILL.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/1500Z 19.6N  46.9W   115 KT
 12HR VT     10/0000Z 20.1N  48.4W   120 KT
 24HR VT     10/1200Z 20.3N  50.3W   125 KT
 36HR VT     11/0000Z 20.2N  52.3W   120 KT
 48HR VT     11/1200Z 19.9N  54.0W   115 KT
 72HR VT     12/1200Z 20.0N  57.0W   115 KT
 96HR VT     13/1200Z 20.5N  60.5W   110 KT
120HR VT     14/1200Z 21.0N  64.5W   110 KT
 
 
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