Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER  37
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT MON SEP 15 2003

ISABEL IS SHOWING STRUCTURAL MIXED SIGNALS THIS EVENING.  ON ONE
SIDE...SATELLITE IMAGERY INDICATES THE EYE REMAINS WELL DEFINED AND
THAT CLOUD TOPS NEAR THE EYE HAVE COOLED DURING THE PAST SEVERAL
HOURS.  ON THE OTHER...REPORTS FROM AN AIR FORCE RESERVE HURRICANE
HUNTER INDICATE THE CENTRAL PRESSURE HAS RISEN TO 940 MB AND THAT
THE MAXIMUM FLIGHT-LEVEL WINDS ARE 138 KT.  THE AIRCRAFT HAS ALSO
REPORTED WELL-DEFINED CONCENTRIC WIND MAXIMA.  SUBJECTIVE SATELLITE
INTENSITY ESTIMATES ARE 115 KT...AS ARE THE LATEST OBJECTIVE
ESTIMATES.  THE MAXIMUM WINDS ARE REDUCED TO 130 KT FOR THIS
ADVISORY...AND THE STORM COULD BE A LITTLE WEAKER THAN THIS.

WHILE THERE HAS BEEN A WOBBLE TO THE LEFT OVER THE PAST FEW HOURS...
THE INITIAL MOTION IS 290/9...THE SAME DIRECTION AS EARLIER.  WATER
VAPOR IMAGERY SHOWS A LARGE ELONGATED RIDGE OF HIGH PRESSURE
EXTENDING FROM SOUTHEASTERN CANADA SOUTHEASTWARD TO EAST OF
ISABEL...AND WESTERLY FLOW WITH SEVERAL EMBEDDED SHORTWAVE TROUGHS
OVER THE CENTRAL AND EASTERN UNITED STATES.  ISABEL SHOULD BEGIN TO
TURN NORTHWESTWARD AROUND THE WEST SIDE OF THE RIDGE DURING THE
NEXT 12-24 HR...THEN GRADUALLY ACCELERATE NORTH-NORTHWESTWARD
BETWEEN THE RIDGE AND THE BROAD TROUGHING TO THE WEST.  ALL
DYNAMICAL MODEL GUIDANCE AGREES WITH THIS SCENARIO...BRINGING
ISABEL TO THE VICINITY OF THE MID-ATLANTIC COAST IN 72-96 HR.  THE
OFFICIAL FORECAST TRACK IS SIMILAR TO...BUT A LITTLE WEST OF THE
PREVIOUS TRACK.  SINCE THE TRACK IS FORECAST TO APPROACH THE COAST
AT A SMALL ANGLE...A SMALL CHANGE IN DIRECTION COULD RESULT IN A
LANDFALL WELL TO THE NORTH OF THE MID-ATLANTIC COAST.  INTERESTS
FROM THE CAROLINAS THROUGH THE NORTHEASTERN STATES SHOULD CLOSELY
MONITOR THE PROGRESS OF ISABEL.

ISABEL IS LIKELY TO CONTINUE IN A WARM-WATER LIGHT-SHEAR ENVIRONMENT
FOR THE NEXT 36 HR...AND THUS FLUCTUATION IN INTENSITY FROM EYEWALL
CONTRACTION CYCLES ARE LIKELY.  BEYOND THAT TIME...THE HURRICANE
WILL BE MOVING INTO THE UPPER-LEVEL SOUTHWESTERLY FLOW ASSOCIATED
WITH THE TROUGH OVER THE UNITED STATES...AND THUS MAY EXPERIENCE
SOME SHEAR.  THE SHIPS MODEL SUGGESTS 30-40 KT OF SHEAR...AND IF
THAT VERIFIES ISABEL COULD WEAKEN CONSIDERABLY.  HOWEVER...THE
LARGE-SCALE MODELS ARE NOT IN AGREEMENT ON THIS...SO THE INTENSITY
FORECAST WILL CALL FOR ONLY A MODEST WEAKENING BEFORE LANDFALL.  IT
SHOULD BE NOTED THAT THE COASTAL SHELF WATER ALONG THE MID-ATLANTIC
COAST IS RATHER COLD...AND ANY TRACK EAST OF CAPE HATTERAS THAT
WOULD KEEP THE HURRICANE OVER THAT WATER WOULD LIKELY PRODUCE MORE
WEAKENING THAN CURRENTLY FORECAST.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      15/0900Z 24.8N  69.0W   130 KT
 12HR VT     15/1800Z 25.5N  70.1W   130 KT
 24HR VT     16/0600Z 26.5N  71.0W   130 KT
 36HR VT     16/1800Z 27.9N  71.9W   125 KT
 48HR VT     17/0600Z 29.2N  72.6W   120 KT
 72HR VT     18/0600Z 33.5N  75.0W   115 KT
 96HR VT     19/0600Z 40.0N  78.0W    60 KT...INLAND
120HR VT     20/0600Z 48.5N  80.0W    35 KT...INLAND EXTRATROPICAL
 
 
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