ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM ISIS DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 8 PM PDT WED SEP 08 2004 THE REASONING FOR THE TRACK FORECAST HAS NOT DEVIATED FROM THE PREVIOUS FORECAST CYCLE...EXCEPT THAT THE INITIAL POSITION HAS BEEN ADJUSTED TO THE NORTH AND EAST AS THE LOW LEVEL CIRCULATION BECAME EXPOSED. THE CENTER WAS EASILY TRACKED FOR SEVERAL HOURS TO GIVE AN INITIAL MOTION OF 335 DEGREES AT 8 KT...A BIT FASTER THAN THE PREVIOUS MOTION. ISIS HAS BEEN EXPERIENCING RATHER SEVERE EASTERLY SHEAR THROUGHOUT THE DAY TODAY WITH THE MAIN CONVECTIVE AREA STILL LOCATED WELL WEST OF THE LOW LEVEL CIRCULATION. THERE WAS SOME INDICATION IN THE LAST FEW VISIBLE SATELLITE FRAMES THAT NEW CONVECTION WAS DEVELOPING NEAR THE LOW LEVEL VORTEX. CLARIFICATION OF THE ACTUAL CENTER POSITION AND MOTION PROVIDES SUFFICIENT EVIDENCE THAT ISIS WILL EXIT THE HIGH VERTICAL SHEAR ENVIRONMENT A BIT EARLIER THAN ANTICIPATED JUST A FEW HOURS AGO. SEA SURFACE TEMPERATURES ALONG THE FORECAST TRACK WILL REMAIN AT LEAST 28 DEG C THROUGH 48 HOURS...AND VERTICAL SHEAR IS FORECASTED TO DECREASE. INTENSITY GUIDANCE IS MORE IN LINE AS THE GFDL MODEL HAS SUDDENLY TAKEN A LIKING TO ISIS. THE SHIPS MODEL ALSO FORECASTS STRENGTHENING AND IS NOW MORE CONSERVATIVE THAN THE GFDL. BASED ON THIS GUIDANCE AND THE MORE NORTHERLY INITIAL MOTION...THE INTENSITY FORECAST IS SLIGHTLY MORE AGGRESSIVE THAN THE PREVIOUS FORECAST. THE TRACK FORECAST IS FAIRLY STRAIGHT FORWARD. ISIS WILL BEGIN TO SLOW DOWN AND TAKE A GRADUAL TURN TOWARD THE NORTHWEST AND THEN WEST-NORTHWEST AS IT ENCOUNTERS A STRONG SUB-TROPICAL RIDGE TO THE NORTH. AN INCREASE IN FORWARD SPEED SHOULD OCCUR LATER IN THE FORECAST PERIOD AS THE RIDGE STRENGTHENS. ISIS SHOULD SLOWLY WEAKEN AFTER THE 72 HOUR FORECAST PERIOD AS IT MOVES OVER SUB 26 DEG C WATER...REMAINING IN A WEAK VERTICAL SHEAR ENVIRONMENT. FORECASTER BEVEN/HENNON FORECAST POSITIONS AND MAX WINDS INITIAL 09/0300Z 16.6N 111.5W 35 KT 12HR VT 09/1200Z 17.0N 111.9W 40 KT 24HR VT 10/0000Z 17.6N 113.5W 45 KT 36HR VT 10/1200Z 18.1N 115.4W 50 KT 48HR VT 11/0000Z 18.5N 118.0W 60 KT 72HR VT 12/0000Z 19.3N 123.5W 55 KT 96HR VT 13/0000Z 19.8N 129.4W 50 KT 120HR VT 14/0000Z 20.3N 136.1W 40 KT $$ NNNN
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Page last modified: Thursday, 09-Sep-2004 02:54:39 UTC