ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM ISIS DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 8 AM PDT SUN SEP 12 2004 A 12/0746Z TRMM PASS DEPICTED THAT THE LOW-LEVEL CIRCULATION CENTER HAS REMAINED PARTIALLY EXPOSED...ABOUT 20 NM TO THE NORTHEAST OF THE DEEP CONVECTION. SATELLITE CURRENT INTENSITY ESTIMATES FROM ALL AGENCIES REMAIN AT 45 KT. THE INITIAL INTENSITY WILL REMAIN AT 45 KT EVEN THOUGH A TRMM PASS 24 HOURS AGO INDICATED THAT THE LOW CLOUD LINES WERE BETTER DEFINED THAN THIS MORNING'S IMAGE. THE SHIPS INTENSITY MODEL CONTINUES TO INDICATE LIGHT 5 KT NORTHEAST TO EAST SHEAR OVER THE NEXT 36 HOURS. HOWEVER...THE UW-CIMSS WIND SHEAR ANALYSIS REVEALS 10 TO 20 KT OF EASTERLY SHEAR WHICH JUSTIFIES THE CURRENT DECOUPLED STRUCTURE OF ISIS. ALTHOUGH THE SLOW INTENSIFICATION TREND THAT SHIPS AND THE GFDL INDICATE SEEMS REASONABLE...INCREASING THE INTENSITY TO 60 KT IN 48 HOURS MAY BE A BIT TOO GENEROUS. THEREFORE...THE INTENSITY TREND FOLLOWS BOTH MODELS THROUGH THE ENTIRE FORECAST PERIOD BUT IS KEPT AT 55 KT BEYOND 48 HOURS. THE INITIAL MOTION IS WESTWARD OR 270/9. ALL DYNAMICAL MODELS CONTINUE TO SHOW A SIGNIFICANT REDUCTION IN SPEED BEYOND 72 HOURS AS A WEAKNESS DEVELOPS IN THE RIDGE NORTH OF ISIS. THE OFFICIAL FORECAST CALLS FOR A PERSISTENT WESTWARD MOTION THROUGH THE ENTIRE FORECAST WITH A SIGNIFICANT DECREASE IN FORWARD SPEED BY DAY 4. THIS AGREES WITH THE MODEL CONSENSUS AND IS SIMILAR TO THE PREVIOUS FORECAST. FORECASTER ROBERTS/BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 12/1500Z 17.4N 123.8W 45 KT 12HR VT 13/0000Z 17.4N 125.1W 50 KT 24HR VT 13/1200Z 17.4N 127.0W 50 KT 36HR VT 14/0000Z 17.4N 129.0W 50 KT 48HR VT 14/1200Z 17.4N 131.0W 55 KT 72HR VT 15/1200Z 17.4N 133.0W 55 KT 96HR VT 16/1200Z 17.4N 134.0W 55 KT 120HR VT 17/1200Z 17.4N 134.5W 55 KT $$ NNNN
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Page last modified: Sunday, 12-Sep-2004 14:44:40 UTC