000 WTPZ44 KNHC 100231 TCDEP4 TROPICAL STORM FLOSSIE DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092007 800 PM PDT THU AUG 09 2007 SATELLITE IMAGERY INDICATES THAT FLOSSIE HAS CHANGED LITTLE IN ORGANIZATION WITH OCCASIONAL GLIMPSES OF A FORMATIVE EYE AND AN EYEWALL FEATURE IN MICROWAVE IMAGERY. DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB REMAIN AT 55 KT...AND SO DOES THE OFFICIAL ADVISORY INTENSITY. IN THE SHORT-TERM...THE INTENSITY FORECAST HAS BECOME COMPLICATED BY THE DEVELOPMENT OF STRONG UPPER-LEVEL EASTERLY FLOW NOW APPROACHING FLOSSIE FROM THE EAST. THE GLOBAL MODELS ARE UNDERESTIMATING THIS FLOW POSSIBLY LEADING TO AN OPTIMISTIC SHEAR FORECAST. ARRESTED DEVELOPMENT COULD RESULT IF THIS STRONG EASTERLY FLOW CATCHES THE CYCLONE...AND FLOSSIE COULD CURRENTLY BE AT OR VERY NEAR ITS PEAK INTENSITY. TO MAINTAIN SOME CONTINUITY WITH THE PREVIOUS ADVISORY...THE INTENSITY FORECAST ALLOWS FOR SLIGHT STRENGTHENING DURING THE DIURNAL CONVECTIVE MAXIMUM LATER TONIGHT...AND THERE IS STILL A CHANCE FLOSSIE COULD BECOME A HURRICANE. BY THE END OF THE FORECAST PERIOD...THE EUROPEAN AND UKMET MODELS SHOW THE DEVELOPMENT OF SIGNIFICANT WESTERLY SHEAR WHICH IS NOT SHOWN IN THE GFS. ACCORDINGLY...THE OFFICIAL FORECAST IS BELOW THE GFS-BASED SHIPS MODEL. THE PRIMARY STEERING MECHANISM CONTINUES TO BE A STRONG RIDGE EXTENDING WESTWARD FROM MEXICO RESULTING IN A MOTION JUST SOUTH OF DUE WEST OR 265/13. FLOSSIE IS EXPECTED TO MAINTAIN A WESTWARD TO WEST-NORTHWESTWARD TRACK THROUGH THE FORECAST PERIOD AS A NARROW RIDGE REMAINS NORTH OF THE CYCLONE. MODEL GUIDANCE IS GENERALLY SPLIT INTO TWO CAMPS BASED ON THE EVENTUAL DEPTH AND STEERING OF THE CYCLONE. THE NOGAPS AND EUROPEAN MODELS...BOTH OF WHICH SHOW A WEAK VORTEX...LIE ON THE SOUTH SIDE OF THE MODEL SUITE. CONVERSELY...THE GFDL AND HWRF MODELS...WHICH SHOW FLOSSIE BECOMING A HURRICANE...LIE ON THE NORTH SIDE OF THE GUIDANCE ENVELOPE. WHILE THE PRESENT TRENDS IN SATELLITE IMAGERY MAKE IT IS TEMPTING TO LEAN TOWARDS THE WEAKER NOGAPS/EUROPEAN SOLUTION...IT IS TOO SOON TO MAKE SUCH A SIGNIFICANT CHANGE TO THE TRACK FORECAST. ACCORDINGLY...THE OFFICIAL FORECAST IS LARGELY UNCHANGED FROM THE PREVIOUS ADVISORY. FORECAST POSITIONS AND MAX WINDS INITIAL 10/0300Z 12.6N 133.7W 55 KT 12HR VT 10/1200Z 12.7N 135.6W 60 KT 24HR VT 11/0000Z 13.0N 137.8W 60 KT 36HR VT 11/1200Z 13.4N 139.8W 60 KT 48HR VT 12/0000Z 13.8N 141.8W 55 KT 72HR VT 13/0000Z 14.5N 146.0W 55 KT 96HR VT 14/0000Z 15.5N 150.5W 50 KT 120HR VT 15/0000Z 16.5N 155.0W 40 KT $$ FORECASTER RHOME