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#152454 (Received by flhurricane at: 6:08 PM 25.Sep.2007) TCDAT3 TROPICAL DEPRESSION THIRTEEN SPECIAL DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL132007 615 PM EDT TUE SEP 25 2007 DATA FROM AN AIR FORCE RECONNAISSANCE AIRCRAFT SHOW THAT THE AREA OF LOW PRESSURE IN THE SOUTHWESTERN GULF OF MEXICO HAS A WELL-DEFINED CIRCULATION. CONVECTION ASSOCIATED WITH THE CENTER HAS COME IN PULSES...WITH SUFFICIENT REGULARITY FOR THE LOW TO QUALIFY AS A TROPICAL DEPRESSION. THE INITIAL INTENSITY OF 25 KT IS BASED ON MAXIMUM FLIGHT-LEVEL WINDS OF 29 KT IN THE SOUTHWEST QUADRANT. THE AIRCRAFT FIXES HAVE BEEN JUMPING AROUND A BIT...BUT A LONGER-TERM MOTION ESTIMATE IS 220/3. THE DEPRESSION IS IN A WEAK STEERING ENVIRONMENT...AND LITTLE OVERALL MOTION IS EXPECTED FOR THE NEXT DAY OR TWO. AFTER THAT...GLOBAL MODELS SUGGEST THAT MID-LEVEL HIGH PRESSURE WILL BUILD OVER THE CENTRAL GULF...AND THIS PATTERN SHOULD BEGIN TO NUDGE THE CYCLONE TO THE SOUTHWEST. THERE IS STILL SOME SOUTHWESTERLY SHEAR OVER THE CYCLONE ASSOCIATED WITH AN UPPER LOW ALONG THE MEXICAN COAST NEAR TAMPICO. THIS SHEAR IS EXPECTED TO RELAX AND BE REPLACED BY AN UPPER ANTICYCLONE OVER THE NEXT COUPLE OF DAYS...WHICH WOULD ALLOW THE SYSTEM AN OPPORTUNITY TO STRENGTHEN. NONE OF THE DYNAMICAL MODELS... INCLUDING THE HWRF AND GFDL...SHOW MUCH DEVELOPMENT...ALTHOUGH THE STATISTICAL SHIPS MODEL TAKES THE SYSTEM TO NEAR HURRICANE STRENGTH IN THREE DAYS. THE OFFICIAL FORECAST BLENDS THIS GUIDANCE BUT IS CLOSER TO THE SHIPS SOLUTION. FORECAST POSITIONS AND MAX WINDS INITIAL 25/2215Z 21.7N 95.0W 25 KT 12HR VT 26/0600Z 21.4N 95.0W 30 KT 24HR VT 26/1800Z 21.2N 95.0W 35 KT 36HR VT 27/0600Z 21.0N 95.0W 40 KT 48HR VT 27/1800Z 20.8N 95.1W 45 KT 72HR VT 28/1800Z 20.5N 95.5W 55 KT 96HR VT 29/1800Z 20.0N 97.0W 50 KT...INLAND 120HR VT 30/1800Z...DISSIPATED $$ FORECASTER FRANKLIN |