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| #108839 (Received by flhurricane at: 10:40 AM 05.Sep.2006) TCDAT1 TROPICAL STORM FLORENCE DISCUSSION NUMBER 8 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062006 1100 AM EDT TUE SEP 05 2006 CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY INDICATE THAT TD-6 HAS CONTINUED TO BECOME BETTER ORGANIZED AND HAS INTENSIFIED INTO VERY LARGE TROPICAL STORM FLORENCE. THE INITIAL INTENSITY OF 35 KT IS BASED ON WIND DATA FROM 05/0836Z QUIKSCAT AND 05/1002 SSMI OVERPASSES THAT REVEALED LARGE PATCHES OF 30-35 KT UNCONTAMINATED WINDS IN THE NORTHWEST QUADRANT. IT COULD BE ARGUED THAT STRONGER WINDS EXIST IN THE NORTHEAST QUADRANT...BUT THAT ASSESSMENT CAN WAIT UNTIL THE NEXT ADVISORY PACKAGE TO SEE IF CONVECTION PERSISTS. THE INITIAL MOTION ESTIMATE IS 290/11. THE AFOREMENTIONED QUIKSCAT OVERPASS AND ALSO ONE AT 04/2130Z NOW CLEARLY INDICATE THAT THE BROAD CIRCULATION CENTER IS FARTHER SOUTH BY AT LEAST 40 NMI THAN INDICATED IN PREVIOUS ADVISORIES. THE ADVISORY POSITION IS ROUGHLY MIDWAY BETWEEN TWO SMALLER CIRCULATIONS -- ONE IN THE NORTHWESTERN QUADRANT AND ONE IN THE SOUTHEASTERN QUADRANT THAT PASSED BY NOAA BUOY 41041 EARLIER THIS MORNING. OTHER THAN RELOCATING THE CENTER FARTHER TO THE SOUTH...THE FORECAST REASONING REMAINS UNCHANGED FROM THE PREVIOUS SEVERAL ADVISORIES. THE NEW FORECAST TRACK IS ALONG THE EXTREME SOUTHERN EDGE OF THE NHC MODEL GUIDANCE ENVELOPE ...WHICH IS MAINLY TO ACCOUNT FOR THE MORE SOUTHERLY INITIAL POSITION. THE LARGE SUBTROPICAL RIDGE TO THE NORTH THAT WILL BE THE MAIN STEERING MECHANISM FOR THE NEXT 4-5 DAYS IS EXPECTED TO KEEP FLORENCE MOVING IN A WEST-NORTHWESTWARD DIRECTION. BY DAY 5...ALL OF THE GLOBAL MODELS CONTINUE TO INSIST THAT A WEAK SHORTWAVE TROUGH WILL BEGIN TO ERODE THE RIDGE TO NORTH OF FLORENCE AND ALLOW THE SYSTEM TO TURN TOWARD THE NORTHWEST AND INTO THE WEAKNESS. THE VERDICT IS STILL OUT ON THE SCENARIO GIVEN THE RELATIVE WEAKNESS OF THE SHORTWAVE TROUGH INDICATED IN THE MODEL WIND FIELDS. SINCE FLORENCE HAS A RATHER LARGE WIND FIELD THAT IS AT LEAST 400 NMI IN DIAMETER ALONG WITH A RADIUS OF MAXIMUM WINDS OF 90-100 NMI...ONLY SLOW INTENSIFICATION IS EXPECTED FOR THE NEXT 48-72 HOURS. AFTER THAT...THE INNER CORE WIND FIELD IS EXPECTED TO CONTRACT IN THE PRESENCE OF LOWER VERTICAL WIND SHEAR AND OVER 29C SSTS...WHICH SHOULD ALLOW FOR MORE SIGNIFICANT STRENGTHENING TO OCCUR. THE ONLY REASON THAT THE INTENSITY FORECAST DOES NOT CALL FOR FLORENCE TO BECOME A MAJOR HURRICANE BY 120 HOURS AS INDICATED BY THE GFDL AND FSU SUPERENSEMBLE MODELS IS THE UNCERTAINTY IN EXACTLY HOW THE UPPER-LEVEL FLOW REGIME WILL EVOLVE BY THAT TIME. ALL OF THE MODELS INDICATE THAT FLORENCE WILL BE NEAR A NARROW 200 MB ANTICYCLONE...BUT THE EXACT POSITION OF THE CYCLONE RELATIVE TO THAT UPPER-LEVEL RIDGE WILL BE CRITICAL IN DETERMINING JUST HOW INTENSE FLORENCE COULD BECOME BY THAT TIME. THE INTENSITY FORECAST REMAINS CONSERVATIVE AND IS SLIGHTLY LOWER THAN THE SHIPS MODEL. FORECAST POSITIONS AND MAX WINDS INITIAL 05/1500Z 17.3N 47.3W 35 KT 12HR VT 06/0000Z 17.9N 48.9W 40 KT 24HR VT 06/1200Z 18.6N 50.9W 45 KT 36HR VT 07/0000Z 19.3N 53.0W 50 KT 48HR VT 07/1200Z 20.1N 55.3W 55 KT 72HR VT 08/1200Z 21.6N 59.5W 65 KT 96HR VT 09/1200Z 23.3N 63.8W 75 KT 120HR VT 10/1200Z 25.5N 67.5W 85 KT $$ FORECASTER STEWART |
