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Hurricane ISABEL (Text)

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HURRICANE ISABEL DISCUSSION NUMBER  45
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT WED SEP 17 2003
 
REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT AND
SATELLITE IMAGERY INDICATE THAT ISABEL HAS CHANGED LITTLE IN
STRENGTH OR ORGANIZATION DURING THE PAST 6 HR.  THE LATEST CENTRAL
PRESSURE REPORTED BY THE AIRCRAFT IS 958 MB...AND THE MAXIMUM 700
MB WINDS THUS FAR ARE 103 KT.  THE AIRCRAFT IS REPORTING A 25-NM
WIDE EYE SIMILAR TO A FEATURE SEEN IN SATELLITE IMAGERY. HOWEVER...
THE AIRCRAFT FIXES ARE SOUTHWEST OF THE SATELLITE FIXES...AND THERE
IS NO WIND MAXIMUM ASSOCIATED WITH THE APPARENT EYEWALL.  INDEED...
THE RADIUS OF MAXIMUM WINDS IS 50-70 NM.  THE MAXIMUM WINDS REMAIN
95 KT FOR THIS ADVISORY.

THE INITIAL MOTION IS NOW 335/8.  THERE IS NO CHANGE IN THE FORECAST
TRACK PHILOSOPHY FROM THE PREVIOUS ADVISORY.  ISABEL SHOULD
CONTINUE TO TRACK GENERALLY NORTH-NORTHWESTWARD BETWEEN A DEEP-
LAYER RIDGE OVER THE WESTERN ATLANTIC AND A DEVELOPING MID/UPPER-
LEVEL TROUGH OVER THE SOUTHEASTERN UNITED STATES.  THE DYNAMICAL
MODELS ARE VERY TIGHTLY CLUSTERED AROUND A LANDFALL IN EASTERN
NORTH CAROLINA IN ABOUT 36 HR...AND THE OFFICIAL FORECAST IS DOWN
THE MIDDLE OF THIS GUIDANCE.  AFTER LANDFALL...ISABEL SHOULD TRACK
NORTH-NORTHWESTWARD OR PERHAPS NORTHWESTWARD FOR 12 HR OR SO...THEN
RECURVE NORTHWARD AND NORTHEASTWARD IN FRONT OF THE STRONG DEEP-
LAYER TROUGH MOVING EASTWARD ACROSS THE NORTHERN UNITED STATES. 
THE NEAR-UNANIMOUS GUIDANCE MAKES THIS A HIGH CONFIDENCE
FORECAST...BUT THOSE AWAY FROM THE FORECAST TRACK SHOULD NOT LET
DOWN THEIR GUARD JUST IN CASE THE GUIDANCE PROVES TO BE UNANIMOUSLY
WRONG.

THE INTENSITY FORECAST REMAINS VERY PROBLEMATIC.  ISABEL CURRENTLY
LACKS A TIGHT CENTRAL CORE AND STRONG CONVECTION...AND EVEN IN
FAVORABLE CONDITIONS WOULD LIKELY BE SLOW TO INTENSIFY.  VERTICAL
SHEAR AND POSSIBLY DRY AIR STILL SEEM TO BE AFFECTING THE
SYSTEM...SO ANY SIGNIFICANT STRENGTHENING WOULD LIKELY HAVE TO WAIT
FOR AT LEAST 12 HR UNTIL THE NEGATIVELY-TILTED SHORTWAVE TROUGH
DEVELOPS OVER THE SOUTHEASTERN UNITED STATES AND IMPROVES THE
OUTFLOW.  EVEN THEN...THERE IS A QUESTION OF WHETHER THE SHEAR WILL
DECREASE ENOUGH TO ALLOW STRENGTHENING.  AN ADDITIONAL COMPLICATION
IS A SURFACE FRONT BETWEEN ISABEL AND THE NORTH CAROLINA COAST...
WITH OBSERVATIONS IN THE HURRICANE WARNING AREA OF COOL AIR WITH
DEWPOINTS BELOW 20C.  INGESTING THAT AIR WOULD LIKELY INHIBIT
STRENGTHENING.  THE INTENSITY FORECAST WILL REMAIN 95 KT UNTIL
LANDFALL BASED MAINLY ON THE PREMISE THAT THE LARGE AND SPRAWLING
VORTEX WILL BE SLOW TO RESPOND TO CHANGES IN THE ENVIRONMENT...
EITHER FAVORABLE OR UNFAVORABLE.  HOWEVER...OTHER POSSIBLE
SCENARIOS INCLUDE STRENGTHENING DUE TO FORCING FROM THE TROUGH...
AND WEAKENING DUE TO VERTICAL SHEAR AND COLD AIR INTRUSION.
  
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      17/0900Z 29.4N  72.2W    95 KT
 12HR VT     17/1800Z 30.8N  73.0W    95 KT
 24HR VT     18/0600Z 33.0N  74.6W    95 KT
 36HR VT     18/1800Z 35.2N  76.4W    95 KT...INLAND
 48HR VT     19/0600Z 38.2N  78.2W    60 KT...INLAND
 72HR VT     20/0600Z 46.5N  78.5W    35 KT...INLAND EXTRATROPICAL
 96HR VT     21/0600Z 57.5N  69.5W    30 KT...INLAND EXTRATROPICAL
120HR VT     22/0600Z...MERGED WITH EXTRATROPICAL LOW
 
 
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