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#455458 (Received by flhurricane at: 7:45 PM 01.Sep.2011) TCDAT3 TROPICAL DEPRESSION THIRTEEN SPECIAL DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132011 700 PM CDT THU SEP 01 2011 SATELLITE...SURFACE...AND NOAA RECONNAISSANCE AIRCRAFT DATA INDICATE THAT THE LOW PRESSURE AREA OVER THE CENTRAL GULF OF MEXICO HAS ACQUIRED A CLOSED CIRCULATION THAT IS DEFINED ENOUGH TO BE CONSIDERED A TROPICAL DEPRESSION. HOWEVER...THE CENTRAL REGION STILL CONSISTS OF A LARGE AREA OF LIGHT WINDS. THE AIRCRAFT DATA AND BUOY OBSERVATIONS SUPPORT AN INITIAL INTENSITY OF 30 KT. ALTHOUGH THERE IS WIND SHEAR OVER THE CYCLONE...AN UPPER-LEVEL ANTICYCLONE IS FORECAST TO BUILD OVER THE GULF OF MEXICO DURING THE NEXT DAY OR SO. THIS SHOULD PROVIDE A MORE FAVORABLE UPPER-LEVEL ENVIRONMENT FOR STRENGTHENING. HOWEVER...SINCE THE CIRCULATION IS LARGE ONLY GRADUAL STRENGTHENING IS ANTICIPATED. THE OFFICIAL INTENSITY FORECAST FOLLOWS THIS REASONING AND IS CLOSE TO THE SHIPS/LGEM GUIDANCE. SINCE THE DEPRESSION IS IN ITS FORMATIVE STAGE THE INITIAL MOTION IS HIGHLY UNCERTAIN. IN FACT...THE CENTER COULD REFORM WITHIN THE LARGE CIRCULATION DURING THE NEXT 12-24 HOURS. THE DEPRESSION IS CURRENTLY LOCATED TO THE SOUTH OF A MID/UPPER LEVEL RIDGE OVER THE CENTRAL UNITED STATES. THE RIDGE IS FORECAST TO SLIDE EASTWARD AND WEAKEN DURING THE NEXT 2-3 DAYS...LEAVING THE CYCLONE IN WEAK STEERING FLOW. THE OFFICIAL FORECAST SHOWS A SLOW NORTHWESTWARD MOTION DURING THE NEXT 24 HOURS...FOLLOWED BY A TURN TOWARD THE NORTH AND NORTHEAST. THE NHC TRACK IS IN BEST AGREEMENT WITH THE GFS AND ECMWF MODELS. THE DEPRESSION IS EXPECTED TO MOVE VERY SLOWLY DURING THE NEXT 5 DAYS PROLONGING THE PERIOD OF TROPICAL STORM CONDITIONS AND HEAVY RAINFALL OVER PORTIONS OF THE NORTHERN GULF COAST. FORECAST POSITIONS AND MAX WINDS INIT 02/0000Z 26.6N 91.4W 30 KT 35 MPH 12H 02/0600Z 27.5N 92.3W 35 KT 40 MPH 24H 02/1800Z 28.2N 92.6W 40 KT 45 MPH 36H 03/0600Z 28.7N 92.7W 45 KT 50 MPH 48H 03/1800Z 29.3N 92.6W 50 KT 60 MPH 72H 04/1800Z 30.1N 92.3W 40 KT 45 MPH...INLAND 96H 05/1800Z 31.1N 91.5W 30 KT 35 MPH...INLAND 120H 06/1800Z 32.0N 90.5W 25 KT 30 MPH...INLAND $$ FORECASTER BROWN/AVILA |