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| #146049 (Received by flhurricane at: 4:43 AM 15.Aug.2007) TCDAT4 TROPICAL STORM DEAN DISCUSSION NUMBER 8 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042007 500 AM EDT WED AUG 15 2007 THE CENTRAL CONVECTION ASSOCIATED WITH DEAN HAS MORE OF A BANDED APPEARANCE THIS MORNING...ALTHOUGH THE BANDING IS NOT YET WELL-DEFINED. WHILE VERTICAL WIND SHEAR HAS DECREASED...IT MAY BE THAT A COMBINATION OF DRY AIR SEEN IN WATER VAPOR IMAGERY NEAR THE STORM AND INFLOW FROM OVER THE COOLER WATERS TO THE NORTH ARE SLOWING AN INCREASE IN CONVECTIVE ORGANIZATION. THE INITIAL INTENSITY REMAINS 45 KT BASED ON CONTINUITY FROM THE EARLIER QUIKSCAT DATA AND THE PREVIOUS ADVISORY. THE INITIAL MOTION IS A SLIGHTLY UNCERTAIN 275/16...UNCERTAIN DUE TO AMSU MICROWAVE DATA HINTING THAT THE CENTER IS A LITTLE SOUTH OF THE ADVISORY POSITION. WATER VAPOR IMAGERY INDICATES THAT DEAN IS ON THE SOUTH SIDE OF A DEEP-LAYER RIDGE... WITH A LARGE MID/UPPER-LEVEL TROUGH COVERING THE ATLANTIC AND CARIBBEAN BETWEEN 64W-77W. THE LARGE-SCALE MODELS SUGGEST THAT THE TROUGH SHOULD GRADUALLY FILL DURING THE FORECAST PERIOD...WITH RIDGING PERSISTING NORTH OF DEAN. THIS SHOULD RESULT IN A GENERAL WESTWARD TO WEST-NORTHWESTWARD MOTION. THERE HAVE BEEN SOME CHANGES IN THE MODEL GUIDANCE...AS THE CANADIAN AND ECMWF MODELS HAVE SHIFTED FROM A WEST-NORTHWESTWARD TRACK TOWARD THE BAHAMAS TO A MORE WESTWARD MOTION THROUGH THE CARIBBEAN. THE UKMET CONTINUES TO CALL FOR A GENERAL WESTWARD MOTION...WHILE THE GFS CALLS FOR A WEST- NORTHWESTWARD MOTION NEAR THE END OF THE FORECAST PERIOD. THE NEW FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK THROUGH 72 HR...THEN SHIFTED A LITTLE WEST OF THE PREVIOUS TRACK THEREAFTER BASED ON THE OVERALL CHANGE IN THE ENVELOPE OF GUIDANCE. THE NEW TRACK IS IN BEST AGREEMENT WITH...BUT A LITTLE SLOWER THAN...THE GFS. DEAN SHOULD ENCOUNTER WARMER SEA SURFACE TEMPERATURES ALONG THE FORECAST TRACK...AND THE VERTICAL SHEAR IS FORECAST TO BE LIGHT DURING THE FORECAST PERIOD. THE INTENSITY GUIDANCE CALLS FOR STEADY STRENGTHENING...AND SO DOES THE INTENSITY FORECAST IN BEST AGREEMENT WITH THE ICON CONSENSUS. GIVEN THE FAVORABLE UPPER-LEVEL WINDS AND WARM WATER...THERE IS A POSSIBILITY THAT DEAN COULD BE NOTABLY STRONGER THAN FORECAST BY THE END OF THE FORECAST PERIOD. FORECAST POSITIONS AND MAX WINDS INITIAL 15/0900Z 12.2N 44.2W 45 KT 12HR VT 15/1800Z 12.4N 46.6W 50 KT 24HR VT 16/0600Z 12.8N 50.1W 55 KT 36HR VT 16/1800Z 13.2N 53.7W 60 KT 48HR VT 17/0600Z 13.8N 57.1W 70 KT 72HR VT 18/0600Z 15.0N 63.0W 80 KT 96HR VT 19/0600Z 16.0N 68.5W 90 KT 120HR VT 20/0600Z 17.5N 74.0W 100 KT $$ FORECASTER BEVEN |
