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#113930 (Received by flhurricane at: 4:55 PM 01.Oct.2006) TCDAT4 HURRICANE ISAAC DISCUSSION NUMBER 17 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092006 500 PM EDT SUN OCT 01 2006 ISAAC REMAINS A FAIRLY WELL-DEFINED HURRICANE IN SATELLITE IMAGERY THIS AFTERNOON. VISIBLE IMAGERY SHOWS A BANDING TYPE EYE AND A INFRARED IMAGERY DEPICTS AN IMPRESSIVE CDO FEATURE WITH TOPS AS COLD AS -70C. A BLEND OF DVORAK CURRENT INTENSITY AND DATA T-NUMBERS SUPPORTS AN INITIAL INTENSITY OF 70 KT. INCREASING SHEAR AND SIGNIFICANTLY COOLER SSTS ALONG THE FORECAST TRACK OF ISAAC ARE EXPECTED TO GRADUALLY WEAKEN THE TROPICAL CYCLONE DURING THE NEXT 24 HOURS. THEREAFTER...ISSAC IS FORECAST TO BECOME A STRONG EXTRATROPICAL CYCLONE AS A BAROCLINIC SYSTEM WILL LIKELY PROVIDE ADDITIONAL ENERGY AFTER ISAAC LOSES ITS TROPICAL CHARACTERISTICS. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY. ISAAC HAS TURNED NORTHWARD AND IS ACCELERATING. THE INITIAL MOTION ESTIMATE IS 005/18 KT. ISAAC IS EXPECTED TO CONTINUE ACCELERATING NORTH-NORTHEASTWARD AHEAD OF A LARGE DEEP-LAYER TROUGH THAT IS EXITING THE EAST COAST OF THE UNITED STATES. TRACK MODEL GUIDANCE HAS SHIFTED CONSIDERABLY WESTWARD AND ALL THE MODELS NOW SHOW LANDFALL IN NEWFOUNDLAND. THE UKMET AND GFS REMAIN ON THE WEST SIDE OF THE MODEL GUIDANCE WHILE THE NOGAPS AND GFDL ARE TO THE EAST...AND FORECAST A TRACK NEAR CAPE RACE NEWFOUNDLAND. THE OFFICIAL TRACK WAS ADJUSTED WEST OF THE PREVIOUS ADVISORY AND IS ALONG THE GUNA MODEL CONSENSUS. AS WAS THE CASE THIS MORNING... AFTER THE PASSAGE OVER NEWFOUNDLAND...THE MODELS CONTINUE TO DIVERGE ON WHICH LOW BECOMES DOMINANT...THE EXTRATROPICAL REMNANT OF ISAAC OR THE BAROCLINIC LOW DEVELOPING OFF THE NORTHEAST UNITED STATES COAST. THIS FORECAST ASSUMES THE SMALLER ISAAC WILL BECOME ABSORBED BY THE LARGE BAROCLINIC LOW AND THE 72 HOUR FORECAST CONTINUES TO REFLECT THIS SCENARIO. REGARDLESS OF WHETHER ISAAC IS A TROPICAL OR EXTRATROPICAL CYCLONE WHEN PASSING NEAR OR OVER NEWFOUNDLAND...IT WILL LIKELY PRODUCE SUSTAINED WINDS OF TROPICAL STORM FORCE OVER THAT AREA. FORECAST POSITIONS AND MAX WINDS INITIAL 01/2100Z 36.3N 60.0W 70 KT 12HR VT 02/0600Z 39.7N 59.1W 65 KT 24HR VT 02/1800Z 45.1N 56.2W 60 KT...EXTRATROPICAL 36HR VT 03/0600Z 49.5N 52.0W 55 KT...EXTRATROPICAL 48HR VT 03/1800Z 52.5N 47.0W 50 KT...EXTRATROPICAL 72HR VT 04/1800Z...ABSORBED $$ FORECASTER BROWN/FRANKLIN |