000 WTPZ42 KNHC 170240 TCDEP2 TROPICAL STORM FAUSTO DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP072008 800 PM PDT WED JUL 16 2008 THE CENTER IS VERY DIFFICULT TO LOCATE...BUT IS BELIEVED TO BE NEAR THE NORTHERN EDGE OF THE MAIN CONVECTIVE BLOB. A BLEND OF THE MOST RECENT DVORAK CLASSIFICATIONS GIVES 40 KT FOR THE INITIAL INTENSITY...ALTHOUGH GIVEN THE UNCERTAIN CENTER LOCATION I AM NOT ESPECIALLY CONFIDENT IN THIS ASSESSMENT. NORTHEASTERLY SHEAR IS HAMPERING DEVELOPMENT...AND THE GLOBAL MODELS SUGGEST THAT THIS COULD REMAIN A FACTOR FOR THE NEXT FEW DAYS. THERE IS CONSIDERABLE SPREAD IN THE INTENSITY GUIDANCE. THE SHIPS MODEL IS MOST AGGRESSIVE...BRINGING FAUSTO TO ABOUT 80 KT IN 3 DAYS...WHILE THE HWRF SHOWS VIRTUALLY NO STRENGTHENING AT ALL. IN BETWEEN ARE THE LGEM AND GFDL MODELS...WITH WHICH THE OFFICIAL FORECAST IS IN GOOD AGREEMENT. THE SHIPS MODEL DIAGNOSES ONLY 10 KT OF SHEAR FROM THE GFS ANALYSIS...WHICH SEEMS UNREALISTICALLY LOW GIVEN THE CURRENT CLOUD PATTERN AND UPPER-LEVEL SATELLITE WINDS. THE INITIAL MOTION IS A HIGHLY UNCERTAIN 280/20. IT APPEARS THAT THIS MORE RAPID MOTION MAY BE THE RESULT OF THE CIRCULATION CENTER ROTATING WITHIN A LARGER CYCLONIC GYRE...OR PERHAPS THERE IS A PROPAGATION COMPONENT TOWARD THE SHEARED CONVECTION. IN EITHER EVENT...I DO NOT EXPECT THIS RAPID MOTION TO PERSIST. THE TRACK FORECAST PHILOSOPHY IS UNCHANGED FROM THE PREVIOUS ADVISORY...AND CALLS FOR FAUSTO TO MOVE WEST-NORTHWESTWARD TO THE SOUTH OF THE SUBTROPICAL RIDGE. THE ECMWF IS AN INTERESTING OUTLIER... THOUGH...TAKING FAUSTO ABOUT 300 NM TO THE NORTHWEST OF THE OTHER MODELS BY 5 DAYS. THIS APPEARS TO BE DUE TO THE FORECAST AMPLIFICATION OF A MID-LEVEL VORTICITY MAX CURRENTLY OVER EXTREME WESTERN TEXAS AS IT MOVES WESTWARD TOWARD THE BAJA PENINSULA. THIS FEATURE THEN PLAYS A ROLE IN BREAKING DOWN THE SUBTROPICAL RIDGE WEST OF BAJA IN ABOUT 3-4 DAYS. THE EVOLUTION OVER THE COLD WATERS WEST OF BAJA IN PARTICULAR SEEMS UNREALISTIC...SO FOR THE MOMENT...THIS SCENARIO IS BEING DISCOUNTED. FORECAST POSITIONS AND MAX WINDS INITIAL 17/0300Z 11.8N 101.7W 40 KT 12HR VT 17/1200Z 12.2N 104.0W 45 KT 24HR VT 18/0000Z 12.9N 106.3W 50 KT 36HR VT 18/1200Z 13.5N 108.4W 55 KT 48HR VT 19/0000Z 13.9N 110.2W 60 KT 72HR VT 20/0000Z 15.0N 113.0W 65 KT 96HR VT 21/0000Z 16.5N 116.5W 70 KT 120HR VT 22/0000Z 18.0N 121.0W 65 KT $$ FORECASTER FRANKLIN