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Chill falls over the Atlantic as the official season heads towards close
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| #6587 (Received by flhurricane at: 11:03 PM 29.Aug.2004) TCDAT1 HURRICANE FRANCES DISCUSSION NUMBER 21 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT SUN AUG 29 2004 THE FIRST RECONNAISSANCE MISSION WAS IN THE HURRICANE FOR SEVERAL HOURS ENDING AT 23Z. THE LAST CENTRAL PRESSURE WAS 954 MB...UP FROM 949 MB A FEW HOURS EARLIER. 954 MB CORRESPONDS TO ABOUT 108 KT. THE HIGHEST 700 MB FLIGHT LEVEL WIND REPORTED WAS 118 KT AT A POSITION ABOUT 9 N MI NORTHWEST OF THE CENTER...90 PERCENT OF 118 KT REDUCES TO A SURFACE WIND OF 106 KT. THERE WERE SEVERAL GPS DROPSONDES NEAR THE EYEWALL. THE HIGHEST SURFACE WIND DETERMINED FROM THESE DROPS WAS 107 KT USING APPROPRIATE REDUCTION TECHNIQUES. THEREFORE THE MAXIMUM WIND IN FRANCES IS REDUCED FROM 115 TO 110 KT. THE SHIPS MODEL FORECASTS THE WIND NEAR 110 KT THROUGH 72 HOURS AND THEN REDUCES IT TO UNDER 100 KT AFTER 72 HOURS. THE GFDL IS SIMILAR. THE GFS AND UKMET ARE MORE AGGRESSIVE BUT THESE MODELS ARE NOT AS SKILLFUL AS THE SHIPS AND GFDL. THE OFFICIAL WIND SPEED FORECAST IS 110 KT THROUGH 120 HOURS AS A COMPROMISE OF THE ABOVE GUIDANCE...REALIZING THAT OUR SKILL AT INTENSITY FORECASTING LEAVES SOMETHING TO BE DESIRED...ESPECIALLY AT LONGER FORECAST PERIODS. THE INITIAL MOTION ESTIMATE IS 275/07. THE GLOBAL TRACK GUIDANCE MODELS SHOW A MOSTLY WESTWARD TRACK FOR 24 TO 36 HOURS FOLLOWED BY A WEST-NORTHWESTWARD TRACK THROUGH 120 HOURS WITH THE SUBTROPICAL RIDGE HOLDING TO THE NORTH OF THE HURRICANE. THE MODELS ARE IN FAIRLY GOOD AGREEMENT ABOUT THIS SCENARIO ALTHOUGH THE GFS IS 50 TO 100 N MI SOUTH OF THE OTHER MODELS THROUGH 72 HOURS BUT THEN COMES INTO BETTER AGREEMENT BY 120 HOURS WHEN ALL OF THE MODELS TEND TO CONVERGE ON THE NORTHERN BAHAMAS. THE OFFICIAL FORECAST TRACK IS ADJUSTED SLIGHTLY SOUTH OF THE PREVIOUS ADVISORY THROUGH 72 HOURS AND IS SIMILAR TO IT AT 96 AND 120 HOURS. NOAA HAS FLOWN A SYNOPTIC SCALE MISSION TONIGHT AND DATA FROM THIS MISSION IS BEING USED TO INITIALIZE THE 00Z MODEL RUNS. THIS HOPEFULLY IMPROVED GUIDANCE WILL BE AVAILABLE FOR THE NEXT ADVISORY PACKAGE. FORECASTER LAWRENCE FORECAST POSITIONS AND MAX WINDS INITIAL 30/0300Z 18.9N 56.2W 110 KT 12HR VT 30/1200Z 19.1N 58.2W 110 KT 24HR VT 31/0000Z 19.5N 60.8W 110 KT 36HR VT 31/1200Z 20.0N 63.4W 110 KT 48HR VT 01/0000Z 20.8N 66.2W 110 KT 72HR VT 02/0000Z 22.5N 71.0W 110 KT 96HR VT 03/0000Z 24.5N 74.5W 110 KT 120HR VT 04/0000Z 26.5N 77.0W 110 KT |
