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#539869 (Received by flhurricane at: 5:02 PM 03.Sep.2012) TCDAT3 TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132012 500 PM EDT MON SEP 03 2012 THE SMALL LOW PRESSURE SYSTEM LOCATED OVER THE CENTRAL ATLANTIC...WHICH DEVELOPED FROM AN UPPER-LEVEL TROUGH...HAS GRADUALLY ACQUIRED ENOUGH ORGANIZED DEEP CONVECTION TO BE CLASSIFIED AS A TROPICAL DEPRESSION. VISIBLE SATELLITE IMAGERY AND AN EARLIER ASCAT PASS INDICATED THAT THE LOW HAS A WELL-DEFINED CENTER AND RELIABLE WINDS OF AROUND 25 KT. THE INITIAL INTENSITY IS SET A LITTLE HIGHER AT 30 KT SINCE ASCAT HAS A KNOWN LOW BIAS AND BECAUSE THE RESOLUTION OF THE INSTRUMENT LIKELY CAN NOT RESOLVE THE SMALL RADIUS OF MAXIMUM WINDS. THE DEPRESSION CURRENTLY LIES BENEATH A TROUGH AXIS...WHERE THE UPPER-LEVEL WINDS APPEAR RELATIVELY LIGHT. GLOBAL MODELS SHOW THE TROUGH AND THE CYCLONE MOVING IN TANDEM...WHICH KEEPS THE DEPRESSION IN A MARGINALLY FAVORABLE UPPER-LEVEL WIND PATTERN FOR A DAY OR SO. THEREFORE...SOME SLIGHT STRENGTHENING IS SHOWN IN THE SHORT TERM. BY LATE WEDNESDAY...THE TROUGH IS EXPECTED TO LIFT OUT AND WEAKEN. THIS WILL CAUSE AN INCREASE IN NORTHWESTERLY SHEAR...AND WILL LIKELY RESULT IN WEAKENING. THE SYSTEM IS EXPECTED TO DEGENERATE TO A REMNANT LOW IN A FEW DAYS. THE DEPRESSION IS FORECAST TO MOVE SLOWLY WEST-NORTHWESTWARD AROUND THE SOUTHWESTERN PORTION OF A RIDGE OVER THE EASTERN ATLANTIC DURING THE NEXT 24 HOURS. AFTER THAT TIME...THE CYCLONE IS EXPECTED TO TURN NORTHWARD AS THE WESTERN PORTION OF THE RIDGE ERODES. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 25.6N 42.2W 30 KT 35 MPH 12H 04/0600Z 25.8N 42.9W 35 KT 40 MPH 24H 04/1800Z 26.4N 43.7W 35 KT 40 MPH 36H 05/0600Z 27.3N 44.3W 35 KT 40 MPH 48H 05/1800Z 28.0N 44.5W 30 KT 35 MPH 72H 06/1800Z 28.5N 44.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 07/1800Z 29.5N 44.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 08/1800Z 30.5N 44.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ FORECASTER BROWN/CANGIALOSI |