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| #110466 (Received by flhurricane at: 4:34 PM 12.Sep.2006) TCDAT3 TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER 2 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 500 PM EDT TUE SEP 12 2006 SATELLITE IMAGES SHOW THAT THE DEPRESSION IS GRADUALLY BECOMING MORE ORGANIZED WITH FAIRLY PROMINENT BANDING FEATURES OVER THE WESTERN AND SOUTHERN PORTIONS OF THE CIRCULATION. HOWEVER THE CENTER IS STILL RATHER BROAD AND ELONGATED...AND THE AREA OF CONVECTION TO THE WEST OF THE CENTER IS MOVING WESTWARD AND BECOMING MORE SEPARATED FROM THE CENTER OF THE CYCLONE. A SHIP REPORT FROM A VESSEL WITH CALL SIGN OVZV2 OF NORTHERLY WINDS OF 36 KT AND A PRESSURE OF 1008.7 MB SOME 180 N MI NORTHWEST OF THE ESTIMATED CENTER OF THE TROPICAL CYCLONE. THIS WIND OBSERVATION WAS IN CONVECTION...PROBABLY A LOCALIZED SQUALL...AND NOT REPRESENTATIVE OF THE STRENGTH OF THE CIRCULATION. MOREOVER...A QUALITY CONTROL CHECK OF THIS SHIP BY THE OCEAN PREDICTION CENTER INDICATED THAT ITS WIND MEASUREMENTS WERE A FEW KNOTS TOO HIGH AND ITS PRESSURE HAS BEEN RUNNING 1-2 MB LOW. HAVING SAID ALL THAT...THE SYSTEM IS NEARING TROPICAL STORM STATUS AND WILL PROBABLY BE NAMED TONIGHT OR ON WEDNESDAY. MODEST EASTERLY SHEAR CURRENTLY PREVAILS OVER THE AREA...AND SINCE THE SEA SURFACE TEMPERATURES ARE FAIRLY WARM... STRENGTHENING SEEMS LIKELY IN THE SHORT TERM. GLOBAL MODELS DIFFER IN THE DETAILS OF THE EVOLUTION OF AN UPPER-LEVEL TROUGH NEAR 40-45W NORTH OF 15N...BUT IN GENERAL THEY SUGGEST THAT IT WILL BECOME LESS INFLUENTIAL IN SEVERAL DAYS. THE SHIPS MODEL...USING THE GFS FORECAST FIELDS AS INPUT...SHOWS WEAK SHEAR THROUGH THE FORECAST PERIOD. I AM NOT TOTALLY CONFIDENT THAT THE UPPER-LEVEL ENVIRONMENT WILL REMAIN SO FAVORABLE...SO THE OFFICIAL INTENSITY FORECAST IS MORE CONSERVATIVE THAN THE SHIPS OUTPUT AND JUST SLIGHTLY BELOW THE CONSENSUS OF THE GUIDANCE. A SLIGHT SOUTHWARD RELOCATION OF THE CENTER HAS BEEN DONE FOR THIS PACKAGE...CONSISTENT WITH MICROWAVE IMAGERY...AND THE FORWARD SPEED HAS BEEN ADJUSTED TO BE A LITTLE SLOWER. CURRENT MOTION IS ESTIMATED TO BE 270/13. DYNAMICAL GUIDANCE INDICATES AN INCREASE IN FORWARD SPEED OVER THE NEXT COUPLE OF DAYS...SUGGESTING A STRENGTHENING OF THE MID-LEVEL RIDGE TO THE NORTH OF THE CYCLONE. BY DAY 3 HOWEVER...THE GUIDANCE INDICATES THAT THE SYSTEM WILL RESPOND TO A WEAKNESS IN THE RIDGE NEAR OR JUST WEST OF 50W...AND BEGIN TO TURN TOWARD THE RIGHT. THE LATEST GFS...U.K. MET OFFICE...NOGAPS...AND ECMWF GLOBAL MODELS ARE IN BETTER AGREEMENT ON THE TRACK AT DAYS 4 AND 5. THE OFFICIAL TRACK FORECAST HAS BEEN SHIFTED SOUTHWARD FROM THE PREVIOUS ONE FOR THE FIRST COUPLE OF DAYS BUT IS ADJUSTED A LITTLE TO THE NORTH IN THE LATTER PART OF THE FORECAST PERIOD. THIS IS NEAR THE LEFT EDGE OF THE TRACK GUIDANCE ENVELOPE. FORECAST POSITIONS AND MAX WINDS INITIAL 12/2100Z 12.0N 23.9W 30 KT 12HR VT 13/0600Z 12.0N 26.3W 40 KT 24HR VT 13/1800Z 12.3N 29.5W 45 KT 36HR VT 14/0600Z 12.6N 33.1W 50 KT 48HR VT 14/1800Z 13.3N 36.7W 60 KT 72HR VT 15/1800Z 15.5N 42.0W 70 KT 96HR VT 16/1800Z 17.5N 46.0W 85 KT 120HR VT 17/1800Z 20.0N 50.0W 95 KT $$ FORECASTER PASCH |
