ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM 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 NNNN
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Page last modified: Monday, 07-Feb-2005 16:49:59 UTC