265 
 WTNT41 KNHC 271433
 TCDAT1
 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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