ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM ISIS DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 2 PM PDT WED SEP 08 2004 VISIBLE AND MICROWAVE IMAGERY THIS AFTERNOON INDICATES THAT THE CYCLONE WAS A LITTLE BIT EAST OF EARLIER ESTIMATES...ON THE NORTHEAST EDGE OF THE DEEP CONVECTION. THIS MEANS A SLOWER INITIAL MOTION ESTIMATE...275/6. DVORAK INTENSITY ESTIMATES FROM BOTH TAFB AND SAB HAVE REACHED 35 KT...AND SO THE DEPRESSION IS UPGRADED TO TROPICAL STORM ISIS. THE 12Z MODELS APPEARED TO HAVE A BETTER INITIALIZATION OF THE VORTEX. THE GFDL...NOGAPS...AND GFS STILL START ISIS OFF TO THE NORTH OR NORTHWEST...AND THE LAST FEW IMAGES ARE SUGGESTIVE OF A NORTHWARD COMPONENT OF MOTION. IF THE STORM MAINTAINS VERTICAL CONTINUITY IT WOULD MOVE MORE WESTWARD WITH THE STRONG UPPER-LEVEL EASTERLY FLOW HOWEVER...AND THAT IS THE SCENARIO FOLLOWED BY THE OFFICIAL FORECAST. REGARDLESS...ALL GUIDANCE MAINTAINS ENOUGH OF A SUBTROPICAL RIDGE NORTH OF ISIS TO PRODUCE A WEST-NORTHWEST TRACK AFTER 24 HOURS. THE OFFICIAL FORECAST IS IN BEST AGREEMENT WITH THE UKMET MODEL. ISIS IS BATTLING 25 KT OF EASTERLY SHEAR...AND THE LOW-LEVEL CENTER IS SOMEWHAT ELONGATED NE-SW. GLOBAL MODELS MAINTAIN OR EVEN INCREASE THE SHEAR SLIGHTLY AS THE UPPER-LEVEL HIGH OVER BAJA BUILDS SOUTHWESTWARD. THE GFDL KEEPS ISIS AS A WEAK SYSTEM WHILE THE SHIPS GUIDANCE BRINGS THE CYCLONE UP TO ABOUT 60 KT. IF ISIS SURVIVES THE NEXT 36 HOURS...IT COULD BECOME A STRONG TROPICAL STORM. LATE IN THE FORECAST PERIOD ISISIS EXPECTED TO MOVE OVER SUB 26C WATER AND BEGIN TO SLOWLY WEAKEN. AN ALTERNATIVE SCENARIO IS THAT ISIS BECOMES SHEARED AND DISSIPATES WITHIN THE NEXT DAY OR SO. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 08/2100Z 15.3N 111.3W 35 KT 12HR VT 09/0600Z 15.7N 112.3W 35 KT 24HR VT 09/1800Z 16.2N 114.0W 40 KT 36HR VT 10/0600Z 16.9N 116.0W 45 KT 48HR VT 10/1800Z 17.5N 118.0W 50 KT 72HR VT 11/1800Z 18.5N 123.0W 55 KT 96HR VT 12/1800Z 19.0N 129.0W 50 KT 120HR VT 13/1800Z 19.5N 135.5W 40 KT $$ NNNN
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Page last modified: Wednesday, 08-Sep-2004 20:24:16 UTC