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Tropical Depression EIGHTEEN (Text)

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TROPICAL DEPRESSION EIGHTEEN DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT SUN SEP 18 2005
 
THE DEPRESSION CONTINUES TO ORGANIZE...WITH GRADUALLY INCREASING
BANDING FEATURES IN THE NORTHEASTERN SEMICIRCLE.  DVORAK INTENSITY
ESTIMATES AT 12Z WERE UNANIMOUSLY 30 KT... AND THIS IS THE NEW
ADVISORY INTENSITY.  AN UPPER LEVEL LOW CURRENTLY CENTERED OVER
WESTERN CUBA...WITH A TROUGH EXTENDING NORTHWARD...CONTINUES TO
IMPOSE THE SOUTHERLY SHEAR ON THE DEPRESSION THAT IS CAUSING THE
ASYMMETRIC CLOUD PATTERN.  HOWEVER...DYNAMICAL MODELS FORECAST THIS
UPPER LOW/TROUGH FEATURE TO WEAKEN...ALLOWING AN EAST-WEST ORIENTED
UPPER LEVEL RIDGE TO BUILD OVER FLORIDA AND THE NORTHERN BAHAMAS
WITHIN THE NEXT TWO DAYS OR SO.  THIS PATTERN CHANGE...ALONG WITH
PLENTY WARM OCEAN WATERS...SHOULD PROVIDE AN ENVIRONMENT SOMEWHAT
MORE FAVORABLE FOR STRENGTHENING...AND THE GFS-BASED SHIPS
DIAGNOSES MUCH LESS SHEAR BEGINNING IN ABOUT 24 HOURS.  AS IS OFTEN
THE CASE WITH DEVELOPING SYSTEMS...THE INTENSITY GUIDANCE IS NOT IN
GOOD AGREEMENT.  THE GFDL REMAINS FAIRLY CONSERVATIVE...NOT
FORECASTING THE CYCLONE TO BECOME A HURRICANE UNTIL IT IS WELL INTO
THE GULF OF MEXICO.  HOWEVER...THE SHIPS FORECASTS A 64 KT
HURRICANE IN 48 HOURS...WITH CONTINUED STRENGTHENING
THEREAFTER...AND THE OFFICIAL FORECAST FOLLOWS SUIT.
 
THE INITIAL MOTION ESTIMATE IS 275/10...NEARLY ALONG THE PREVIOUS
ADVISORY TRACK.  HOWEVER...THE SOUTHERLY SHEAR COULD BE FORCING SOME
REDEVELOPMENT OF THE CENTER FARTHER NORTH DURING THE NEXT DAY OR
SO...AND IN FACT IT COULD ALREADY BE SLIGHTLY NORTH OF THE ADVISORY
POSITION.  THERE SHOULD BE SUFFICIENT RIDGING TO FORCE THE TROPICAL
CYCLONE GENERALLY WESTWARD FOR THE NEXT COUPLE OF DAYS...ALTHOUGH
SOME WEST-NORTHWESTWARD MOTION COULD OCCUR DUE TO SOME DOWNSHEAR
REFORMATION OF THE CENTER.  THE NEW FORECAST TRACK IS ADJUSTED
SLIGHTLY NORTH OF THE PREVIOUS ADVISORY THROUGH 36 HOURS...THEN
ALONG THE PREVIOUS TRACK AFTER THAT...EXCEPT FOR INTRODUCING A
WEST-NORTHWESTWARD BEND AT THE END OF THE FORECAST DUE TO MODELS
EXPECTED SOME WEAKENING OF THE RIDGE IN THE WESTERN GULF OF MEXICO.

THE FORECAST WIND RADII HAVE BEEN EXPANDED BASED ON THE CURRENT SIZE
OF THE CIRCULATION AND ON WIND RADII CLIPER GUIDANCE.  BASED ON THE
NEW FORECAST... HURRICANE WATCHES HAVE BEEN ISSUED FOR THE FLORIDA
KEYS.
 
FORECASTER KNABB
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/1500Z 22.0N  72.2W    30 KT
 12HR VT     19/0000Z 22.6N  73.9W    40 KT
 24HR VT     19/1200Z 23.2N  76.2W    45 KT
 36HR VT     20/0000Z 23.7N  78.3W    55 KT
 48HR VT     20/1200Z 23.8N  80.8W    65 KT
 72HR VT     21/1200Z 24.0N  85.5W    75 KT
 96HR VT     22/1200Z 24.0N  90.5W    85 KT
120HR VT     23/1200Z 25.0N  94.0W    90 KT
 
 
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