000 WTPZ44 KNHC 091445 TCDEP4 TROPICAL STORM FLOSSIE DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092007 800 AM PDT THU AUG 09 2007 ALTHOUGH THE AMOUNT OF DEEP CONVECTION WITH FLOSSIE HAS DECREASED SOMEWHAT OVER THE PAST COUPLE OF HOURS...THE CYCLONE IS MAINTAINING WELL-DEFINED CONVECTIVE BANDS IN THE NORTHERN SEMICIRCLE AND A SEPARATE AREA OF DEEP CONVECTION JUST SOUTH OF THE PRESUMED CENTER. GOOD OUTFLOW IS EVIDENT IN ALL QUADRANTS EXCEPT THE EAST. DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB WERE 45 KT...AND THE ADVISORY INTENSITY WILL REMAIN 45 KT. FLOSSIE IS EXPECTED TO REMAIN OVER 27C-PLUS WATERS FOR ABOUT 48 HOURS. GIVEN THE PRESENT BANDING STRUCTURE AND GOOD OUTFLOW... FURTHER DEVELOPMENT IS EXPECTED. THE SHIPS...HWRF...AND GFDL MODELS ALL FORECAST FLOSSIE TO BECOME A HURRICANE. AFTER 48 HOURS...SSTS ALONG THE FORECAST TRACK DECREASE BUT NOT RAPIDLY...AND THE GFS SUGGESTS THAT A FAVORABLE UPPER-LEVEL PATTERN COULD PERSIST EVEN AFTER SSTS BEGIN TO COOL. THIS ARGUES FOR A RELATIVE SLOW WEAKENING TREND DURING DAYS 3-5. THE INITIAL MOTION REMAINS 265/12. FLOSSIE IS NEAR THE SOUTHWESTERN EDGE OF A MID-LEVEL RIDGE...BUT GLOBAL MODELS SUGGEST THAT ENOUGH RIDGING WILL BUILD WESTWARD TO KEEP THE CYCLONE FROM INTERACTING MUCH WITH A MID- TO UPPER-LEVEL TROUGH CURRENTLY NEAR 135W. MODEL GUIDANCE OFFERS TWO BASIC SCENARIOS. THE GFDL...HWRF...AND GFS MAINTAIN A RELATIVELY STRONG SYSTEM ON A WEST-NORTHWESTERLY TRACK...WHILE THE UKMET...ECMWF...AND NOGAPS WEAKEN THE CYCLONE IN A DAY OR TWO AND TAKE IT MORE RAPIDLY WESTWARD IN THE LOW-LEVEL FLOW. ASSUMING FLOSSIE DEVELOPS AS EXPECTED...THE FORMER SCENARIO SEEMS MORE REASONABLE. THE OFFICIAL FORECAST IS VERY SIMILAR TO THE PREVIOUS ADVISORY AND CLOSE TO A BLEND OF THE GFS...GFDL...AND HWRF MODELS. FORECAST POSITIONS AND MAX WINDS INITIAL 09/1500Z 13.0N 130.9W 45 KT 12HR VT 10/0000Z 12.9N 132.7W 50 KT 24HR VT 10/1200Z 13.1N 135.0W 60 KT 36HR VT 11/0000Z 13.3N 137.0W 65 KT 48HR VT 11/1200Z 13.5N 139.0W 65 KT 72HR VT 12/1200Z 14.0N 143.0W 55 KT 96HR VT 13/1200Z 15.0N 147.5W 50 KT 120HR VT 14/1200Z 16.0N 151.5W 45 KT $$ FORECASTER FRANKLIN