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TROPICAL STORM ARLENE DISCUSSION NUMBER  18
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT TUE JUN 15 1999
 
A USAF RESERVE AIRCRAFT FIXED THE STORM RECENTLY.  BASED ON THIS FIX
THE INITIAL MOTION ESTIMATE IS 300/03 ALTHOUGH THE LOW LEVEL CENTER
IS NOT THAT WELL DEFINED.  MOST OF THE GUIDANCE INDICATES
ACCELERATION TOWARD THE NORTH AFTER 48 HOURS AS A MAJOR TROUGH
APPROACHES.  ONLY THE NOGAPS REMAINS SLOW WESTNORTHWESTWARD THROUGH
72 HOURS AND THIS WAS FROM THE 12Z RUN.  THE OFFICIAL FORECAST IS
SHIFTED A SMIDGEON TO THE LEFT OF THE PREVIOUS ADVISORY AND
ACELLERATES THE STORM TO 12 KNOTS AFTER 48 HOURS.

THE AIRCRAFT REPORTED 55 KNOTS AT 1500 FEET ALTITUDE IN THE
NORTHEAST QUADRANT AND DVORAK T NUMBERS ARE 3.0 FROM TAFB AND SAB. 
SO THE WIND SPEED IS INCREASED TO 50 KNOTS ON THIS BASIS.  OTHERWISE
THE INTENSITY FORECAST IS THE SAME AS THE PREVIOUS ADVISORY EXCEPT
FOR ADDING 5 KNOTS AT ALL FORECAST PERIODS AND CALLS FOR GRADUAL
WEAKENING IN 36 HOURS AS COLDER SSTS ARE ENCOUNTERED.

THE 34 KNOTS RADIUS IS INCREASED TO 125 NMI IN THE NORTHEAST
QUADRANT BASED ON AIRCRAFT DATA.  THIS IS EXTENDED TO THE NORTHWEST
QUADRANT IN 24 HOURS AS SATELLITE IMAGERY SHOWS THE DEEP CONVECTION
ROTATING CYCLONICALLY AROUND THE NORTHERN HALF OF THE STORM.

BERMUDA IS RETAINING THE TROPICAL STORM WATCH FOR THIS ADVISORY.

LAWRENCE
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     16/0300Z 30.1N  62.0W    50 KTS
12HR VT     16/1200Z 30.4N  62.7W    50 KTS
24HR VT     17/0000Z 31.1N  63.5W    50 KTS
36HR VT     17/1200Z 32.2N  63.9W    45 KTS
48HR VT     18/0000Z 33.5N  64.5W    40 KTS
72HR VT     19/0000Z 38.0N  64.0W    35 KTS
 
 
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