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Tropical Storm FLORENCE (Text)

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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
 
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