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| #152412 (Received by flhurricane at: 10:34 AM 25.Sep.2007) TCDAT2 TROPICAL STORM KAREN DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122007 1100 AM EDT TUE SEP 25 2007 KAREN IS EXHIBITING SOME BANDING FEATURES ON VISIBLE SATELLITE IMAGERY BUT THE DEEP CONVECTION IS NOT THAT STRONG OR CONCENTRATED NEAR THE CENTER AT THIS TIME. DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB REMAIN AT 35 KT SO THE CURRENT INTENSITY IS UNCHANGED FROM THE PREVIOUS ADVISORY. THE ENVIRONMENT AHEAD OF THE STORM IS QUESTIONABLE FOR STRENGTHENING. KAREN'S UPPER-LEVEL OUTFLOW IS BEING RESTRICTED OVER THE NORTHWEST QUADRANT DUE TO A NEARBY UPPER-LEVEL CYCLONIC SHEAR AXIS. WITHIN THE NEXT FEW DAYS... GLOBAL MODELS DEPICT A COUPLE OF UPPER-LEVEL TROUGHS OVER THE CENTRAL SUBTROPICAL ATLANTIC THAT SHOULD CAUSE INCREASING SOUTHWESTERLY VERTICAL SHEAR OVER THE TROPICAL CYCLONE. THE SHIPS MODEL...USING THE GFS FORECAST...SHOWS THE SHEAR INCREASING TO 20 KT BY 60 HOURS AND MORE THAN 30 KT NEAR THE END OF THE PERIOD. IN SPITE OF THIS SEEMINGLY HOSTILE ENVIRONMENT...SHIPS PREDICTS KAREN TO BECOME A HURRICANE BY 48 HOURS AND TO MAINTAIN HURRICANE STRENGTH ALMOST TO THE END OF THE FORECAST PERIOD. THE LATEST RUN OF THE GFDL MODEL ALSO INTENSIFIES THE TROPICAL STORM INTO A HURRICANE AFTER 72 HOURS. IT IS DIFFICULT TO ACCEPT THIS GUIDANCE IN THE FACE OF SUCH STRONG PREDICTED SHEAR. THEREFORE THE OFFICIAL FORECAST...AS IN THE PREVIOUS PACKAGE...STRENGTHENS KAREN TO JUST BELOW HURRICANE STATUS AND THEN INDICATES WEAKENING AFTER DAY 3. INITIAL MOTION...290/13 THE SAME AS IN THE PREVIOUS ADVISORY. KAREN CONTINUES ON THE SOUTH SIDE OF A LOW- TO MID-LEVEL SUBTROPICAL RIDGE. THIS SCENARIO SHOULD PERSIST FOR THE NEXT DAY OR SO. AFTERWARDS...A MID- TO UPPER-TROPOSPHERIC CYCLONE SHOULD CREATE A WEAKNESS IN THE RIDGE. IF THIS OCCURS...KAREN SHOULD GRADUALLY TURN NORTHWESTWARD AND THEN NORTH-NORTHWESTWARD. THERE CONTINUES TO BE A FAIR AMOUNT OF SPREAD IN THE TRACK GUIDANCE MODELS. THE HWRF AND GFS TRACKS ARE NEAR THE RIGHT SIDE OF THE GUIDANCE ENVELOPE AND THE U.K. MET MODEL TRACK IS NEAR THE LEFT SIDE. THE OFFICIAL FORECAST IS CLOSE TO THE DYNAMICAL CONSENSUS...NOT FAR FROM THE GFDL TRACK...AND FAIRLY SIMILAR TO THE PREVIOUS NHC TRACK. FORECAST POSITIONS AND MAX WINDS INITIAL 25/1500Z 10.8N 38.7W 35 KT 12HR VT 26/0000Z 11.2N 40.7W 40 KT 24HR VT 26/1200Z 11.8N 43.5W 45 KT 36HR VT 27/0000Z 12.5N 46.1W 55 KT 48HR VT 27/1200Z 13.9N 48.3W 60 KT 72HR VT 28/1200Z 17.2N 51.2W 60 KT 96HR VT 29/1200Z 20.0N 53.0W 55 KT 120HR VT 30/1200Z 22.5N 54.0W 55 KT $$ FORECASTER PASCH |
