Hurricane FRANCES

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HURRICANE FRANCES DISCUSSION NUMBER  11
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT FRI AUG 27 2004
 
FRANCES CONTINUES TO BECOME BETTER ORGANIZED WHILE STRENGTHENING TO
90 KT. THE INITIAL INTENSITY IS SUPPORTED BY A DVORAK SATELLITE
INTENSITY ESTIMATE OF T5.0...OR 90 KT...FROM TAFB...A SATELLITE
DATA T-NUMBER OF 5.0 FORM AFWA...AND 27/1010Z UW-CIMSS AMSU
PRESSURE RETRIEVAL OF 969.8 MB...WHICH EQUATES TO ABOUT 90 KT. THE
OUTFLOW REMAINS EXCELLENT AND ALSO CONTINUES TO IMPROVE.
 
THE MOTION IS NOW 300/09. FRANCES REMAINS ON TRACK AND HAS BEGUN TO
SLOW DOWN. A NORTHWESTWARD JOG MAY OCCUR...BUT IT IS EXPECTED TO BE
SHORT-LIVED AS THE WEAKNESS IN THE SUBTROPICAL RIDGE TO THE NORTH
OF FRANCES IS FORECAST TO QUICKLY FILL IN AS THE SHORTWAVE TROUGH
NOTED IN WATER VAPOR IMAGERY ALONG 52W LONGITUDE CONTINUES TO ZIP
ALONG EASTWARD. THE NHC MODEL GUIDANCE IS IN STRONG AGREEMENT ON A
WEST-NORTHWEST TO NORTHWESTWARD TRACK THROUGH 48 HOURS...BUT THEN
DIVERGE SIGNIFICANTLY AFTER THAT. HOWEVER...DESPITE THE DIFFERING
TRACKS...ALL OF THE MODELS AGREE ON HIGH ZONAL FLOW WITH STRONG
WESTERLIES DEVELOPING ACROSS THE NORTHERN U.S. AND THE NORTH
ATLANTIC AFTER 48HR. SUCH A STRONG HIGH-LATITUDE ZONAL FLOW PATTERN
IS USUALLY REFLECTED BY A STRONG SUBTROPICAL RIDGE TO THE SOUTH
THAT EXTENDS EAST-WEST FROM THE AZORES TO BERMUDA AND INTO THE
SOUTHEASTERN U.S.  MY CONCERN IS THAT THE RIDGE MAY BUILD IN FASTER
THAN EXPECTED AND DRIVE FRANCES MORE WESTWARD SOONER THAN FORECAST
...WHICH IS WHAT THE 06Z GFS MODEL IS INDICATING. HOWEVER...MAKING
SUCH A SUDDEN AND SHARP 45 DEGREE LEFT-OF-TRACK TURN AT 48 HOURS IS
PROBABLY OVERDOING IT SOME...BUT OUT OF RESPECT FOR THE CONSISTENT
TREND IN THE GFS MODEL THE PAST 24 HOURS...THE FORECAST TRACK HAS
BEEN NUDGED A LITTLE MORE SOUTH AND WESTWARD IN 72-120HR.

FRANCES IS EXPECTED TO REMAIN IN A LOW SHEAR ENVIRONMENT AND OVER
INCREASING SSTS THROUGHOUT THE PERIOD...SO AT LEAST SOME SLOW
INTENSIFICATION SHOULD OCCUR. THE SHIPS MODEL SHARPLY BRINGS DOWN
THE INTENSITY TO 73 KT AFTER 72 HOURS DUE TO INCREASING WESTERLY
SHEAR OF 25-30 KT. HOWEVER...THE VERTICAL SHEAR IS FICTITIOUS AND
'SELF-INFLICTED' BY THE GFS/SHIPS MODEL...DUE TO THE OFFICIAL
FORECAST TRACK BEING ABOUT 180 NMI NORTH OF THE GFS FORECAST
POSITIONS IN 72-120H. THIS PUTS FRANCES IN THE STRONG WESTERLY FLOW
IN THE NORTHERN SEMICIRCLE OF A VERY INTENSE UPPER-LEVEL HIGH THAT
ALL THE MODELS DEVELOP OVER FRANCES. THE SHIPS MODEL WAS DISCOUNTED
AND THE OFFICIAL INTENSITY FORECAST LEANS TOWARD THE GFDL SOLUTION.

FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/1500Z 15.0N  49.0W    90 KT
 12HR VT     28/0000Z 15.8N  50.4W   100 KT
 24HR VT     28/1200Z 17.0N  52.1W   100 KT
 36HR VT     29/0000Z 18.0N  53.6W   105 KT
 48HR VT     29/1200Z 18.9N  55.2W   105 KT
 72HR VT     30/1200Z 20.2N  58.5W   110 KT
 96HR VT     31/1200Z 21.0N  62.0W   110 KT
120HR VT     01/1200Z 22.0N  67.0W   110 KT
 
 
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