|
Show Selection: |
| #41471 (Received by flhurricane at: 5:11 PM 23.Aug.2005) TCDAT2 TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT TUE AUG 23 2005 DATA FROM AN AIR FORCE RESERVE UNIT RECONNAISSANCE AIRCRAFT...ALONG WITH OBSERVATIONS FROM THE BAHAMAS AND NEARBY SHIPS...INDICATE THE BROAD LOW PRESSURE AREA OVER THE SOUTHEASTERN BAHAMAS HAS BECOME ORGANIZED ENOUGH TO BE CLASSIFIED AS TROPICAL DEPRESSION TWELVE. THE INITIAL INTENSITY OF 30 KT IS BASED RECON WINDS OF 39 KT AT 800 FT...AND SHIP A8CI9 REPORTING 30-KT SUSTAINED WINDS AT 18Z IN THE NORTHEAST QUADRANT. UPPER-LEVEL OUTFLOW IS WEAK...BUT IMPROVING AS A SMALL ANTICYCLONE HAS BEEN DEVELOPING ABOVE THE LOW-LEVEL CENTER. THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 310/07. THE LOW-LEVEL CENTER HAS BEEN REFORMING WITHIN A LARGE CLEAR AREA NOTED IN SATELLITE IMAGERY. HOWEVER...FLIGHT-LEVEL RECON WINDS CLEARLY INDICATE A BROAD BUT OTHERWISE WELL-DEFINED LOW-LEVEL WIND FIELD. THERE HAVE BEEN SEVERAL SMALL VORTICES DEVELOP WITHIN THE CONVECTION IN THE EASTERN SEMICIRCLE AND THEN ROTATE WESTWARD OUT FROM UNDER THE CONVECTION. THE INITIAL POSITION IS ROUGHLY THE GEOMETRIC CENTER OF ALL THE SMALL SWIRLS...BUT SOME RE-ORGANIZATION OF THE CENTER WITHIN THE CONVECTION IS POSSIBLE. TD-12 IS EXPECTED TO CONTINUE MOVING SLOWLY NORTHWESTWARD TOWARD A WEAKNESS IN THE MID-LEVEL SUBTROPICAL RIDGE. THIS WEAKNESS SHOWS UP BEST IN 500 MB DATA...AND THEN DISAPPEARS BELOW AND ABOVE THAT LEVEL. BY 36-48 HOURS...ALL OF THE GLOBAL MODELS AND THE GFDL MODEL FORECAST THE WEAKNESS TO FILL AND BE REPLACED BY A BROAD EAST-WEST ORIENTED RIDGE. THIS SHOULD HELP TO DRIVE THE CYCLONE MORE WESTWARD ACROSS SOUTHERN FLORIDA IN 60-72 HOURS...AND THEN INTO THE EASTERN GULF OF MEXICO BY 96 HOURS. THIS SCENARIO IS CONSISTENT WITH THE NHC MODEL CONSENSUS AND THE DEVELOPING SYNOPTIC PATTERN. THE INTENSITY FORECAST IS A LITTLE TRICKY DUE TO THE UNCERTAINTY ON EXACTLY WHEN A WELL-DEFINED CENTER WILL DEVELOP AND HOW SOON CONVECTION WRAPS AROUND THE WEST SIDE OF THE CIRCULATION. THE UPPER-LEVEL FLOW IS FORECAST TO REMAIN STRONGLY DIFLUENT FROM THE NORTH FOR THE NEXT 24-36 HOURS...AND THEN BECOME NORTHEASTERLY TO EASTERLY AFTER THAT. SINCE THE SHEAR IS ALSO FORECAST TO REMAIN RELATIVELY LOW AT AROUND 10 KT AND SSTS WILL BE NEAR 31C UNDER THE CENTER...AT LEAST STEADY INTENSIFICATION APPEARS TO BE IN ORDER. IF CENTRAL CONVECTION DEVELOPS WITHIN THE NEXT 24 HOURS...THEN THIS SYSTEM COULD REACH HURRICANE STRENGTH BEFORE IT MAKES LANDFALL. THE OFFICIAL INTENSITY FORECAST IS SLIGHTLY LOWER THAN THE SHIPS MODEL. THE NWS RULES GOVERNING THE NAMING OF TROPICAL CYCLONES SPECIFY THAT...WITHIN A BASIN...WHEN A CYCLONE FORMS FROM THE REMNANT OF A PREVIOUSLY EXISTING CYCLONE...THE OLD NAME/NUMBER IS RETAINED. TROPICAL DEPRESSION TWELVE HAS A COMPLEX GENESIS THAT LIKELY INCLUDES A MID-LEVEL REMNANT OF FORMER TROPICAL DEPRESSION TEN. A REVIEW OF SATELLITE AND RAWINSONDE DATA OVER THE PAST WEEK OR SO SUGGESTS THAT A SECOND DISTURBANCE APPROACHED AND COMBINED WITH THE MID-LEVEL REMNANT OF TROPICAL DEPRESSION TEN ON 20 AUGUST. BECAUSE IT IS IMPOSSIBLE TO DETERMINE WHICH OF THESE TWO SYSTEMS IS ASSOCIATED WITH TODAY'S GENESIS...WE HAVE ELECTED TO USE THE DESIGNATION TWELVE RATHER THAN TEN FOR THE NEW DEPRESSION. THIS SITUATION DIFFERS FROM LAST YEAR'S REGENERATION OF IVAN...IN WHICH THE LOW-LEVEL REMNANT OF THAT SYSTEM REMAINED A DISTINCT FEATURE THAT COULD BE FOLLOWED CONTINUOUSLY UNTIL IT REGENERATED. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 23/2100Z 23.2N 75.5W 30 KT 12HR VT 24/0600Z 24.0N 76.5W 35 KT 24HR VT 24/1800Z 25.0N 77.7W 40 KT 36HR VT 25/0600Z 25.7N 78.5W 45 KT 48HR VT 25/1800Z 26.0N 79.4W 60 KT 72HR VT 26/1800Z 26.3N 81.0W 50 KT...INLAND 96HR VT 27/1800Z 26.5N 83.5W 60 KT 120HR VT 28/1800Z 27.5N 86.0W 65 KT |
