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#113959 (Received by flhurricane at: 11:11 PM 01.Oct.2006) TCDAT4 HURRICANE ISAAC DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092006 1100 PM EDT SUN OCT 01 2006 CONVENTIONAL SATELLITE IMAGERY INDICATES THAT ISAAC IS GRADUALLY WEAKENING. THE EYE FEATURE IS NO LONGER EVIDENT AND THE DEEP CONVECTION IS BECOMING LESS SYMMETRIC ABOUT THE CIRCULATION CENTER. THE INITIAL INTENSITY IS LOWERED TO 65 KT BASED ON A BLEND OF THE LATEST DVORAK DATA T AND CI NUMBERS. THE OVERALL INTENSITY FORECAST REASONING REMAINS ESSENTIALLY UNCHANGED. ISAAC WILL SOON BE ENCOUNTERING A SHARP GRADIENT IN SST AS IT CROSSES THE NORTH WALL OF THE GULF STREAM IN 6-12 HOURS. ADDITIONALLY...THE CYCLONE WILL BE ENCOUNTERING INCREASING SOUTHWESTERLY SHEAR. THESE ENVIRONMENTAL FACTORS SHOULD RESULT IN WEAKENING AND A LOSS OF TROPICAL CHARACTERISTICS DURING THE NEXT 24 HOURS. RESTRENGTHENING OF ISAAC AS AN EXTRATROPICAL CYCLONE APPEARS UNLIKELY...SINCE MUCH OF THE AVAILABLE BAROCLINIC ENERGY WILL BE UTILIZED BY ANOTHER LOW PRESSURE SYSTEM CURRENTLY FORMING OFF THE NEW ENGLAND COAST. GIVEN ISAAC'S RELATIVELY SMALL SIZE...THE OFFICIAL FORECAST ASSUMES ISAAC WILL BE ABSORBED BY THE LARGER BAROCLINIC LOW WITHIN 2-3 DAYS. REGARDLESS OF THE EXACT EVOLUTION OF ISAAC...IT IS EXPECTED TO AFFECT NEWFOUNDLAND TOMORROW WITH THE POTENTIAL FOR WINDS OF TROPICAL STORM STRENGTH. ISAAC IS ACCELERATING NORTH-NORTHEASTWARD WITH AN INITIAL MOTION ESTIMATE OF 020/23 KT. THE CYCLONE IS EXPECTED TO TURN TOWARD THE NORTHEAST DURING THE NEXT 24 HOURS...TAKING THE SYSTEM OVER OR VERY NEAR NEWFOUNDLAND TOMORROW. GUIDANCE IS GENERALLY IN GOOD AGREEMENT ON THIS SCENARIO...FOLLOWED BY A TURN TOWARD THE EAST-NORTHEAST AS THE CYCLONE PULLS AWAY FROM NEWFOUNDLAND. THE NEW OFFICIAL FORECAST IS SHIFTED A LITTLE EAST TOWARD THE MODEL CONSENSUS...AND IS SLIGHTLY FASTER THAN THE PREVIOUS ADVISORY. FORECAST POSITIONS AND MAX WINDS INITIAL 02/0300Z 38.6N 58.8W 65 KT 12HR VT 02/1200Z 42.5N 57.2W 60 KT...BECOMING EXTRATROPICAL 24HR VT 03/0000Z 47.8N 53.5W 50 KT...EXTRATROPICAL 36HR VT 03/1200Z 51.5N 49.3W 45 KT...EXTRATROPICAL 48HR VT 04/0000Z 53.3N 45.5W 45 KT...EXTRATROPICAL 72HR VT 05/0000Z...ABSORBED $$ FORECASTER RHOME/KNABB |