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TROPICAL STORM ARLENE DISCUSSION NUMBER  10
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT SUN JUN 13 1999
 
THE INITIAL MOTION ESTIMATE IS 280/04.  THE 18Z AVIATION MODEL
CONTINUES TO SHOW THE STORM EMBEDDED IN A RIDGE.  GUIDANCE MODELS
ARE IN PRETTY GOOD AGREEMENT ABOUT A SLOW NORTHWEST TO NORTHWARD
MOTION FOR THE NEXT THREE DAYS.  THE OFFICIAL FORECAST IS ADJUSTED A
SMIDGEON TO THE LEFT OF THE PREVIOUS ADVISORY...AS ARE THE NOGAPS
AND GFDL MODELS COMPARED TO THEIR PREVIOUS RUNS.  A TROUGH IN THE
WESTERLIES IS FORECAST TO MOVE NORTH OF THE STORM IN THE NEXT THREE
DAYS AND COULD CAUSE SOME NORTHWARD ACCELERATION NEAR THE END OF THE
FORECAST PERIOD...AND THIS IS INDICATED BY THE UKMET MODEL BUT NOT
BY THE NOGAPS OR GFDL.
 
WESTERLY SHEAR CONTINUES TO IMPINGE ON THE WEST SIDE OF THE STORM
AND DVORAK INTENSITY ESTIMATES ARE DOWN TO 3.0 CURRENT INTENSITY
NUMBERS FROM TAFB AND SAB.  THE KGWC ESTIMATE IS 2.5.  U.S. NAVY AND
ECMWF SSM/I AND SCATTEROMETER WIND SPEEDS AROUND THE STORM SHOW WIND
SPEEDS OF LESS THAN 50 KNOTS.  SO THE INITIAL WIND SPEED IS
DECREASED 5 KNOTS TO 45 KNOTS ON THIS BASIS.  THE OFFICIAL FORECAST
WIND SPEEDS ARE ALSO DECREASED 5 KNOTS FROM THE PREVIOUS ADVISORY
IN AGREEMENT WITH SHIPS AND GFLD GUIDANCE.
 
THE CENTRAL SURFACE PRESSURE WHICH WAS PREVIOUSLY ESTIMATED AT 1000
MB IS INCREASED TO 1009 MB BASED ON SHIP REPORTS WHICH SHOW
SURROUNDING PRESSURES TO BE RATHER HIGH.

LAWRENCE

FORECAST POSITIONS AND MAX WINDS
 
INITIAL     14/0300Z 29.3N  59.6W    45 KTS
12HR VT     14/1200Z 29.4N  60.3W    45 KTS
24HR VT     15/0000Z 29.8N  61.2W    50 KTS
36HR VT     15/1200Z 30.3N  61.8W    55 KTS
48HR VT     16/0000Z 31.0N  62.5W    55 KTS
72HR VT     17/0000Z 32.5N  63.0W    55 KTS
 
 
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