ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM HURRICANE ISABEL DISCUSSION NUMBER 47 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT WED SEP 17 2003 IF FLIGHT-LEVEL OBSERVATIONS WERE ALL WE HAD...ISABEL WOULD BE A CATEGORY THREE HURRICANE. THE HURRICANE HUNTER AIRCRAFT THIS AFTERNOON FOUND A NUMBER OF SPOTS OF WINDS OF 110-120 KT. THIS WOULD NORMALLY CORRESPOND TO SURFACE WINDS OF 100-105 KT. HOWEVER...NUMEROUS DROPSONDE PROFILES IN THE HIGH WIND REGIONS OF THE CIRCULATION SHOW A CONSISTENT AND UNUSUALLY STEEP FALL-OFF OF WIND IN THE BOUNDARY LAYER. THIS IS CONSISTENT WITH THE MEAGER CONVECTION IN THE HURRICANE CORE. BASED ON THESE PROFILES...THE INITIAL INTENSITY IS SET AT 90 KT. THE UPPER-LEVEL OUTFLOW PATTERN HAS BECOME FAVORABLE...AS WAS FORECAST BY THE GLOBAL MODELS...AND IN FACT THE CIRCULATION ALOFT IS STRENGTHENING. HOWEVER... THERMODYANAMIC FACTORS ARE LIMITING THE ABILITY OF ISABEL TO COMPLETELY RESPOND TO THE FAVORABLE UPPER-LEVEL FORCING. THE OFFICIAL FORECAST DOES NOT ANTICIPATE ANY SIGNIFICANT INCREASE IN STRENGTH PRIOR TO LANDFALL...BUT SHOULD THERE BE A SUBSTANTIAL INCREASE IN DEEP CONVECTION ISABEL COULD QUICKLY REACH CATEGORY THREE STATUS. ONCE AGAIN...THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE TRACK FORECAST OR REASONING. THE LATEST RUN OF THE GFS IS A LITTLE FASTER AND SLIGHTLY TO THE RIGHT OF THE PREVIOUS RUN...BUT THE GUIDANCE REMAINS IN EXCELLENT AGREEMENT. THE INITIAL MOTION IS NOW 330/12 AS ISABEL BEGINS A MODEST ACCELERATION TOWARD THE COAST. SOME ADDITIONAL ACCELERATION IS STILL EXPECTED PRIOR TO LANDFALL. ISABEL HAS A LARGE CIRCULATION...INCLUDING A LARGE EXTENT OF DAMAGING WINDS. THEREFORE...IT IS ESPECIALLY IMPORTANT NOT TO FOCUS ON THE PRECISE LANDFALL LOCATION...SINCE SIGNIFICANT IMPACTS WILL BE FELT AT LARGE DISTANCES FROM THE LANDFALL POINT. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 17/2100Z 31.1N 73.3W 90 KT 12HR VT 18/0600Z 32.7N 74.4W 95 KT 24HR VT 18/1800Z 35.0N 76.6W 95 KT...INLAND 36HR VT 19/0600Z 37.6N 78.5W 60 KT...INLAND 48HR VT 19/1800Z 41.5N 79.0W 40 KT...INLAND 72HR VT 20/1800Z 52.5N 76.0W 30 KT...EXTRATROPICAL 96HR VT 21/1800Z...ABSORBED BY EXTRATROPICAL LOW NNNN
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Page last modified: Monday, 07-Feb-2005 16:49:59 UTC