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| #461256 (Received by flhurricane at: 4:53 AM 23.Sep.2011) TCDAT1 TROPICAL STORM OPHELIA DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL162011 500 AM AST FRI SEP 23 2011 OPHELIA CONTINUES TO STRUGGLE AGAINST STRONG SOUTHWESTERLY SHEAR. THE CENTER OF THE TROPICAL STORM REMAINS EXPOSED WELL TO THE WEST OF A LARGE CURVED BAND...ALTHOUGH THIS BAND IS AT A CONSIDERABLE DISTANCE FROM THE CENTER. WITH LITTLE CONVECTION NEAR THE CENTER...IT IS LIKELY THE WINDS HAVE DROPPED SINCE THE LAST ADVISORY...AND THE INITIAL WIND SPEED IS 40 KT. FURTHER WEAKENING IS FORECAST DUE TO THE PERSISTENT SHEAR FROM AN UPPER-LEVEL TROUGH...AND THE INTENSITY FORECAST IS LOWERED FROM THE PREVIOUS PREDICTION. IT IS ALSO QUITE POSSIBLE THAT OPHELIA WILL WEAKEN INTO A REMNANT LOW SOMETIME DURING THE NEXT COUPLE OF DAYS. IF OPHELIA SURVIVES...THE UPPER-LEVEL ENVIRONMENT COULD BECOME MORE FAVORABLE FOR STRENGTHENING AT DAYS 4 AND 5...SO SOME INTENSIFICATION IS SHOWN AT THOSE TIMES. THE INITIAL MOTION IS 290/11. A GRADUAL TURN TO THE RIGHT IS ANTICIPATED OVER THE NEXT DAY OR SO AS OPHELIA MOVES AROUND THE SOUTHERN PERIPHERY OF A RIDGE OVER THE WESTERN ATLANTIC OCEAN. THERE ARE SOME RATHER LARGE DIFFERENCES IN THE GLOBAL MODEL TRACKS ALMOST IMMEDIATELY...WHICH SEEM TO BE RELATED TO THE DEPTH OF THE TROPICAL CYCLONE. GENERALLY...THE MODELS THAT SHOW A WEAKER CYCLONE...SUCH AS THE ECMWF...SHOW THE WEST-NORTHWESTWARD MOTION CONTINUING FOR THE NEXT SEVERAL DAYS UNDER THE RIDGE. THE GFS/HWRF/GFDL MODELS HAVE A MORE VERTICALLY COHERENT TROPICAL CYCLONE WHICH IS AFFECTED MORE BY THE SOUTHWESTERLY UPPER-LEVEL FLOW. THIS DEEPER STRUCTURE CAUSES THE CYCLONE TO MOVE TOWARD THE NORTHWEST AND NORTH-NORTHWEST...TO THE RIGHT OF THE BULK OF THE GUIDANCE. GIVEN THAT OPHELIA IS EXPECTED TO WEAKEN AND BECOME MORE SHALLOW...THE NHC FORECAST IS SHIFTED TO THE LEFT...BUT NOT QUITE AS FAR TO THE WEST AS THE ECMWF OR BAM SHALLOW MODELS. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 14.5N 51.0W 40 KT 45 MPH 12H 23/1800Z 15.3N 52.7W 35 KT 40 MPH 24H 24/0600Z 16.7N 55.0W 30 KT 35 MPH 36H 24/1800Z 18.0N 57.0W 30 KT 35 MPH 48H 25/0600Z 19.2N 58.9W 30 KT 35 MPH 72H 26/0600Z 21.0N 62.0W 30 KT 35 MPH 96H 27/0600Z 23.0N 64.5W 35 KT 40 MPH 120H 28/0600Z 25.5N 66.0W 40 KT 45 MPH $$ FORECASTER BLAKE |
