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TROPICAL STORM ARLENE DISCUSSION NUMBER  11
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT MON JUN 14 1999

ARLENE CONTINUES MOVING WEST WITH THE INITIAL MOTION OF 275/05.
LARGER SCALE GUIDANCE IS IN REASONABLE AGREEMENT...WITH BROAD
LOW/MID LEVEL RIDGING NORTHEAST OF ARLENE PRODUCING A GRADUAL TURN
TO THE NORTHWEST/NORTH DURING THE NEXT THREE DAYS. THIS WOULD TAKE
THE CENTER OF ARLENE NEAR OR EAST OF BERMUDA. NHC HURRICANE GUIDANCE
IS MORE DIVERSE...WITH THE BAMS PASSING JUST NORTH OF BERMUDA...THE
GFDL AND BAMM PASSING JUST SOUTH OF BERMUDA...AND THE BAMD...A98E
AND LBAR MAINTAINING A WESTWARD MOTION THROUGH THE PERIOD. THE
OFFICIAL FORECAST IS IN THE MIDDLE OF THE OVERALL GUIDANCE AND
SHIFTED SOMEWHAT TO THE LEFT OF THE PREVIOUS TRACK.

CONVECTION HAS INCREASED NEAR THE CENTER DURING THE NIGHT...
ALTHOUGH THE CENTER REMAINS PARTIALLY EXPOSED DUE TO WESTERLY SHEAR.
THE LATEST INTENSITY ESTIMATES ARE 45 KT FROM TAFB AND SAB...AND 2.5
FROM AFWA. THE CURRENT INTENSITY REMAINS AT 45 KT.

THE QUESTION NOW IS HOW MUCH SHEAR WILL ARLENE ENCOUNTER? THE LATEST
WATER VAPOR WINDS SUGGEST 10-20 KT WESTERLIES WEST OF THE CENTER...
WITH THE SHIPS MODEL INDICATING LESS THAN 15 KT OF SHEAR THROUGH 48
HOURS. AVAILABLE GLOBAL MODELS ALSO SUGGEST A DECREASE IN SHEAR...
WITH A UPPER LEVEL TROUGH DIGGING WEST OF BERMUDA BUILDING A RIDGE
NEAR ARLENE. BASED ON THIS...THE INTENSITY FORECAST IS A LITTLE
STRONGER THAN IN THE PREVIOUS PACKAGE. THE MODELS INDICATE STRONG
NORTHERLY SHEAR DEVELOPING NEAR ARLENE BY 72 HOURS...WHICH IN
COMBINATION WITH COOLER SSTS SHOULD WEAKEN THE SYSTEM BY THAT TIME.
 
WIND RADII AT THE 36-72 HOUR FORECAST TIMES HAVE BEEN ADJUSTED BASED
ON THE PREDICTED NORTHWARD TURN AND HIGH PRESSURE TO THE EAST.

WATCHES OR WARNINGS FOR BERMUDA WILL NEED TO BE CONSIDERED LATER
TODAY.
 
BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     14/0900Z 29.3N  60.2W    45 KTS
12HR VT     14/1800Z 29.4N  61.0W    50 KTS
24HR VT     15/0600Z 29.7N  61.9W    55 KTS
36HR VT     15/1800Z 30.5N  62.8W    60 KTS
48HR VT     16/0600Z 31.5N  63.5W    60 KTS
72HR VT     17/0600Z 33.0N  64.0W    55 KTS
 
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