ZCZC MIATCDAT2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM FRED DISCUSSION NUMBER 2 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072009 1100 PM AST MON SEP 07 2009 A RECENTLY RECEIVED TRMM PASS FROM 2324 UTC SUGGESTS THAT THE CENTER OF THE CYCLONE IS LOCATED FARTHER SOUTH AND CLOSER TO THE DEEP CONVECTION. RECENT INFRARED GEOSTATIONARY IMAGERY SHOWS A CURVED BAND BEGINNING TO WRAP INTO THE LOCATION OF THE SUSPECTED CENTER. BASED ON THIS EVIDENCE...THE DEPRESSION IS UPGRADED TO TROPICAL STORM FRED AND THE INITIAL INTENSITY IS SET TO 35 KT. THE SHIPS MODEL CURRENTLY ANALYZES EASTERLY WIND SHEAR OF ABOUT 15 KNOTS OVER FRED. THIS SHEAR IS FORECAST TO DECREASE IN ABOUT 12 HOURS...AND WITH THE CYCLONE MOVING OVER WARM WATER...THIS SHOULD ALLOW FOR ADDITIONAL STRENGTHENING THROUGH 72 HOURS OR SO. BEYOND THAT TIME...FRED IS EXPECTED TO ENCOUNTER INCREASINGLY SOUTHWESTERLY WIND SHEAR AHEAD OF AN UPPER-LEVEL TROUGH. THE COMBINATION OF THE SHEAR AND COOLER SSTS SHOULD RESULT IN A SLOW WEAKENING AT DAYS 4 AND 5. THE OFFICIAL FORECAST IS ABOVE THE ICON INTENSITY CONSENSUS FOR THE FIRST 24 HOURS GIVEN THE CURRENT SATELLITE TRENDS...AND IS CLOSE TO ICON FROM 24 TO 48 HOURS. BEYOND THAT TIME...THE INTENSITY FORECAST IS CLOSER TO LGEM...SINCE THAT MODEL TYPICALLY HAS A GOOD HANDLE ON THE EFFECTS OF CHANGING ENVIRONMENTAL CONDITIONS LATE IN THE FORECAST PERIOD. THE INITIAL MOTION IS ESTIMATED TO BE 275/13...BUT THIS IS UNCERTAIN GIVEN THE RECENT RELOCATION OF THE CENTER. THE TRACK GUIDANCE REMAINS IN GENERAL AGREEMENT ON TAKING THE CYCLONE ON A WESTWARD TO WEST-NORTHWESTWARD HEADING TO THE SOUTH OF A NARROW SUBTROPICAL RIDGE AXIS FOR ABOUT 48 HOURS. BEYOND THAT TIME...FRED IS EXPECTED TO RECURVE INTO A BREAK IN THE RIDGE BETWEEN 30W AND 35W. AT THE END OF THE PERIOD...MUCH OF THE GUIDANCE SUGGESTS A VERY SLOW NORTHWARD OR NORTH-NORTHWESTWARD MOTION...AS THE MID-TO UPPER-LEVEL TROUGH THAT CAUSES THE BREAK IN THE RIDGE LIFTS OUT...ALLOWING WEAK RIDGING TO BUILD IN NORTH OF FRED. THE OFFICIAL FORECAST TRACK IS SHIFTED SIGNIFICANTLY TO THE SOUTH OF THE PREVIOUS TRACK DUE TO THE MORE SOUTHERLY LOCATION OF THE CENTER. BY THE END OF THE PERIOD...THE OFFICIAL FORECAST SHOWS A TURN TOWARD THE NORTH AND THE NORTH-NORTHWEST WITH A DECREASE IN FORWARD SPEED...IN GOOD AGREEMENT WITH THE TVCN MULTI-MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INITIAL 08/0300Z 11.8N 26.3W 35 KT 12HR VT 08/1200Z 12.0N 28.0W 45 KT 24HR VT 09/0000Z 12.6N 30.0W 50 KT 36HR VT 09/1200Z 13.6N 31.7W 55 KT 48HR VT 10/0000Z 14.8N 32.9W 60 KT 72HR VT 11/0000Z 17.5N 34.0W 55 KT 96HR VT 12/0000Z 19.0N 34.0W 55 KT 120HR VT 13/0000Z 21.0N 34.5W 50 KT $$ FORECASTER BRENNAN NNNN
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Page last modified: Thursday, 31-Dec-2009 12:09:09 UTC