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#108900 (Received by flhurricane at: 4:31 PM 05.Sep.2006) TCDAT1 TROPICAL STORM FLORENCE DISCUSSION NUMBER 9 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062006 500 PM EDT TUE SEP 05 2006 THE LOW-LEVEL CIRCULATION CENTER...AS WELL AS CONVECTIVE BANDING FEATURES HAS BECOME BETTER DEFINED IN VISIBLE SATELLITE IMAGERY. THUNDERSTORM ACTIVITY HAS ALSO BEGUN TO DEVELOP IN THE INNER CORE REGION. GIVEN THE OVERALL IMPROVEMENT IN THE CONVECTIVE STRUCTURE OF FLORENCE...PLUS A 05/1641Z UW-CIMSS AMSU ESTIMATE OF 1003 MB AND 42 KT...THE INITIAL INTENSITY HAS BEEN INCREASED TO 40 KT. THE INITIAL MOTION ESTIMATE IS 290/10. ALL OF THE GLOBAL AND REGIONAL MODELS CONTINUE TO AGREE ON A GENERAL WEST-NORTHWESTWARD MOTION THROUGH 96 HOURS...WITH A TURN TOWARD THE NORTHWEST INTO A DEVELOPING WEAKNESS IN THE SUBTROPICAL RIDGE AFTER THAT. THE MODELS HAVE BEEN VERY PERSISTENT IN DEVELOPING AN EVENTUAL BREAK IN THE RIDGE AXIS BETWEEN 65W-75W FOR THE PAST SEVERAL RUNS. HOWEVER ...EACH RUN HAS SHIFTED THE TRACK A LITTLE FARTHER TO THE WEST. GIVEN THAT THE MID- TO UPPER-LEVEL FLOW IS FORECAST TO BE WEST-SOUTHWESTERLY NORTH OF THE RIDGE AXIS...AND THAT A LARGE MID-LATITUDE TROUGH IS EXPECTED TO DIG INTO THE CENTRAL U.S. BY DAY 5...THE MODELS MAY BE OVERDOING THE AMOUNT OF SHORTWAVE ENERGY FORECAST TO GENERATE THE WEAKNESS IN THE RIDGE. THE OFFICIAL FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS TRACK...AND REMAINS A LITTLE SOUTH OF THE MODEL CONSENSUS AND ALONG THE SOUTHERN PORTION OF THE NHC MODEL GUIDANCE ENVELOPE. ALTHOUGH FLORENCE CONTINUES TO GET BETTER ORGANIZED...IT REMAINS AN UNUSUALLY LARGE ATLANTIC TROPICAL STORM...AND LARGE CYCLONES TEND TO TAKE LONGER TO DEVELOP AND INTENSIFY THAN SMALLER ONES DO. AS A RESULT...ONLY MODEST INTENSIFICATION IS FORECAST FOR THE NEXT 48 HOURS OR SO...WITH A FASTER RATE OF STRENGTHENING INDICATED AFTER THAT AS FLORENCE MOVES OVER 29-29.5C SSTS AND BENEATH DECREASING VERTICAL SHEAR. IF FLORENCE MOVES UNDERNEATH THE CENTER OF A 200 MB ANTICYCLONE LIKE THE NOGAPS...UKMET...AND ECMWF MODELS ARE SUGGESTING...THEN STRENGTHENING INTO A MAJOR HURRICANE LIKE THE GFDL AND FSU SUPERENSEMBLE MODELS ARE FORECASTING WILL BE POSSIBLE. FORECAST POSITIONS AND MAX WINDS INITIAL 05/2100Z 17.4N 48.5W 40 KT 12HR VT 06/0600Z 18.0N 49.9W 45 KT 24HR VT 06/1800Z 18.8N 51.9W 50 KT 36HR VT 07/0600Z 19.7N 54.0W 55 KT 48HR VT 07/1800Z 20.6N 56.5W 60 KT 72HR VT 08/1800Z 22.3N 61.1W 70 KT 96HR VT 09/1800Z 24.3N 65.7W 80 KT 120HR VT 10/1800Z 27.0N 69.0W 90 KT $$ FORECASTER STEWART |