Hurricane FRANCES

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HURRICANE FRANCES DISCUSSION NUMBER  29
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT TUE AUG 31 2004
 
RECENT RECONNAISSANCE AIRCRAFT REPORTS INDICATE THE CENTRAL PRESSURE
HAS STABILIZED TO AROUND 939-940 MB...BASED ON THE 700 MB HEIGHT
FALLS. THE MAXIMUM FLIGHT-LEVEL WIND REPORTED ON THE LAST LEG WAS
130 KT ...WHICH EQUATES TO ABOUT A 117-KT SURFACE WIND. A DROPSONDE
IN THE NORTHEAST QUADRANT ALSO REPORTED A 135-KT WIND AT ABOUT 600
FT ABOVE THE OCEAN SURFACE. CLOUD TOPS HAVE ALSO COOLED AROUND THE
EYE AND THE EYE HAS BECOME MORE DISTINCT IN BOTH SATELLITE AND
RADAR DATA...WHILE CONTRACTING DOWN TO ABOUT 20 NMI. BASED ON THIS
INFORMATION...THE INTENSITY IS BEING MAINTAINED AT 120 KT. 

THE INITIAL MOTION IS NOW 285/14. THE FORECAST IS RELATIVELY CLEAR
CUT THROUGH 48 HOURS WITH MOST OF THE NHC MODEL GUIDANCE AGREEING
ON A WEST-NORTHWESTWARD MOTION TOWARD THE EAST-CENTRAL BAHAMAS.
AFTER THAT...THE MODELS DIVERGE AND DIVIDE INTO THREE DISTINCT TRACK
PATTERNS. THE GFDL AND GFDN RACE FRANCES TOWARD THE SOUTHERN COAST
OF SOUTH CAROLINA IN 96-120 HR...THE GFS...MEDIUM AND DEEP BAM...
AND UKMET MODELS TAKE FRANCES MORE SLOWLY INTO EAST-CENTRAL FLORIDA
IN 96-120 HR...WHILE THE NOGAPS...LBAR..12Z ECMWF...AND THE ETA
MODELS MOVE FRANCES ACROSS SOUTHEAST FLORIDA IN ABOUT 72 HR. THE
18Z GFDL MODEL ALSO SHIFTED WESTWARD FROM THE PREVIOUS RUN. IF THE
GFDN AND GFDL MODELS ARE IGNORED...THE REST OF THE NHC MODEL
GUIDANCE AGREES THAT THE FLORIDA EAST COAST WILL BE THE EVENTUAL
LANDFALL REGION. ONE DISTURBING PIECE OF INFORMATION IS THAT ALL OF
THE MODELS...EXCLUDING THE GFDL AND GFDN...AGREE THAT FRANCES WILL
SLOW DOWN TO LESS THAN 10 KT AFTER 72 HOURS...AND THE GFS EVEN
REDUCES THE FORWARD SPEED TO 4 KT IN 96 HR. THIS SUGGESTS THAT
STEERING CURRENTS MAY BRIEFLY COLLAPSE AS FRANCES APPROACHES THE
NORTHWESTERN BAHAMAS AND THE FLORIDA EAST COAST. THE DIFFERENCE IN
THE MODELS IS HOW THEY HANDLE THE DEEP LOW OFF THE NORTHWESTERN
U.S. COAST AS IT DIGS INTO THE CENTRAL PLAINS...AND HOW THE RIDGE
AMPLIFIES ALONG THE U.S. EAST COAST IN RESPONSE TO THAT DIGGING
LOW/TROUGH. THE GFDL HAS BEEN CONSISTENTLY INITIALIZING TOO WEAK OF
A RIDGE AROUND BERMUDA...SO LITTLE WEIGHT WAS PLACED ON THE
GFDL/GFDN SOLUTIONS. A SLIGHT WESTWARD JOG WAS PLACED IN THE
FORECAST TRACK AFTER 72-96 HR TO INDICATE SOME BUILDING OF THE
RIDGE TO THE NORTH OF FRANCES AT THAT TIME. THE OFFICIAL TRACK IS
CLOSE TO THE PREVIOUS TRACK THROUGH 72 HOURS...AND THEN A LITTLE
LEFT OF TRACK...IN ACCORDANCE WITH THE GUNA CONSENSUS MODEL.
 
THE INTENSITY FORECAST REMAINS UNCHANGED. THE SHIPS MODEL PEAKS
FRANCES AT 124 KT IN 12-24 HOURS...THEN WEAKENS THE HURRICANE DOWN
TO 112 KT IN 72 HOURS. HOWEVER...THIS WEAKENING IS CAUSED BY
'SELF-INFLICTED' VERTICAL SHEAR SINCE THE OFFICIAL FORECAST TRACK
IS SOUTH OF THE GFS TRACK...PLACING THE HURRICANECENTER IN STRONG
CYCLONIC WESTERLY OUTFLOW ON THE SOUTH SIDE OF THE GFS MODEL STORM.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      01/0300Z 20.8N  67.0W   120 KT
 12HR VT     01/1200Z 21.7N  69.1W   125 KT
 24HR VT     02/0000Z 22.8N  71.4W   130 KT
 36HR VT     02/1200Z 24.0N  73.5W   130 KT
 48HR VT     03/0000Z 25.2N  75.5W   130 KT
 72HR VT     04/0000Z 26.8N  78.3W   125 KT
 96HR VT     05/0000Z 28.0N  81.0W   100 KT...INLAND
120HR VT     06/0000Z 31.0N  82.5W    55 KT...INLAND
 
 
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