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| #46741 (Received by flhurricane at: 11:03 AM 18.Sep.2005) TCDAT3 TROPICAL DEPRESSION EIGHTEEN DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT SUN SEP 18 2005 THE DEPRESSION CONTINUES TO ORGANIZE...WITH GRADUALLY INCREASING BANDING FEATURES IN THE NORTHEASTERN SEMICIRCLE. DVORAK INTENSITY ESTIMATES AT 12Z WERE UNANIMOUSLY 30 KT... AND THIS IS THE NEW ADVISORY INTENSITY. AN UPPER LEVEL LOW CURRENTLY CENTERED OVER WESTERN CUBA...WITH A TROUGH EXTENDING NORTHWARD...CONTINUES TO IMPOSE THE SOUTHERLY SHEAR ON THE DEPRESSION THAT IS CAUSING THE ASYMMETRIC CLOUD PATTERN. HOWEVER...DYNAMICAL MODELS FORECAST THIS UPPER LOW/TROUGH FEATURE TO WEAKEN...ALLOWING AN EAST-WEST ORIENTED UPPER LEVEL RIDGE TO BUILD OVER FLORIDA AND THE NORTHERN BAHAMAS WITHIN THE NEXT TWO DAYS OR SO. THIS PATTERN CHANGE...ALONG WITH PLENTY WARM OCEAN WATERS...SHOULD PROVIDE AN ENVIRONMENT SOMEWHAT MORE FAVORABLE FOR STRENGTHENING...AND THE GFS-BASED SHIPS DIAGNOSES MUCH LESS SHEAR BEGINNING IN ABOUT 24 HOURS. AS IS OFTEN THE CASE WITH DEVELOPING SYSTEMS...THE INTENSITY GUIDANCE IS NOT IN GOOD AGREEMENT. THE GFDL REMAINS FAIRLY CONSERVATIVE...NOT FORECASTING THE CYCLONE TO BECOME A HURRICANE UNTIL IT IS WELL INTO THE GULF OF MEXICO. HOWEVER...THE SHIPS FORECASTS A 64 KT HURRICANE IN 48 HOURS...WITH CONTINUED STRENGTHENING THEREAFTER...AND THE OFFICIAL FORECAST FOLLOWS SUIT. THE INITIAL MOTION ESTIMATE IS 275/10...NEARLY ALONG THE PREVIOUS ADVISORY TRACK. HOWEVER...THE SOUTHERLY SHEAR COULD BE FORCING SOME REDEVELOPMENT OF THE CENTER FARTHER NORTH DURING THE NEXT DAY OR SO...AND IN FACT IT COULD ALREADY BE SLIGHTLY NORTH OF THE ADVISORY POSITION. THERE SHOULD BE SUFFICIENT RIDGING TO FORCE THE TROPICAL CYCLONE GENERALLY WESTWARD FOR THE NEXT COUPLE OF DAYS...ALTHOUGH SOME WEST-NORTHWESTWARD MOTION COULD OCCUR DUE TO SOME DOWNSHEAR REFORMATION OF THE CENTER. THE NEW FORECAST TRACK IS ADJUSTED SLIGHTLY NORTH OF THE PREVIOUS ADVISORY THROUGH 36 HOURS...THEN ALONG THE PREVIOUS TRACK AFTER THAT...EXCEPT FOR INTRODUCING A WEST-NORTHWESTWARD BEND AT THE END OF THE FORECAST DUE TO MODELS EXPECTED SOME WEAKENING OF THE RIDGE IN THE WESTERN GULF OF MEXICO. THE FORECAST WIND RADII HAVE BEEN EXPANDED BASED ON THE CURRENT SIZE OF THE CIRCULATION AND ON WIND RADII CLIPER GUIDANCE. BASED ON THE NEW FORECAST... HURRICANE WATCHES HAVE BEEN ISSUED FOR THE FLORIDA KEYS. FORECASTER KNABB FORECAST POSITIONS AND MAX WINDS INITIAL 18/1500Z 22.0N 72.2W 30 KT 12HR VT 19/0000Z 22.6N 73.9W 40 KT 24HR VT 19/1200Z 23.2N 76.2W 45 KT 36HR VT 20/0000Z 23.7N 78.3W 55 KT 48HR VT 20/1200Z 23.8N 80.8W 65 KT 72HR VT 21/1200Z 24.0N 85.5W 75 KT 96HR VT 22/1200Z 24.0N 90.5W 85 KT 120HR VT 23/1200Z 25.0N 94.0W 90 KT |
