Tropical Storm BILL

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TROPICAL STORM BILL DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SUN JUN 29 2003
 
REPORTS FROM AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT THIS
AFTERNOON INDICATE THAT LOW LEVEL CIRCULATION CENTER IS NOT VERY
WELL DEFINED.  THIS MAKES THE INITIAL MOTION RATHER UNCERTAIN.  THE
INITIAL MOTION ESTIMATE IS 335/11.  THE TRACK GUIDANCE IS IN GOOD
AGREEMENT ABOUT TURNING THE STORM NORTH AND THEN EASTWARD AROUND
THE WESTERN PERIPHERY OF A MID LEVEL HIGH PRESSURE RIDGE EXTENDING
EASTWARD FROM THE EASTERN GULF OF MEXICO.  HOWEVER THE GUIDANCE
ALSO SHIFTS THE TRACKS EASTWARD ABOUT 100 N MI FROM THE PREVIOUS
ADVISORY AND SO DOES THE OFFICIAL FORECAST.  THIS IS PARTIALLY DUE
TO SHIFTING THE INITIAL POSITION EASTWARD.  THIS ALSO REQUIRES AN
EASTWARD SHIFT TO THE WATCH AREA WHICH WILL ALSO BE CHANGED TO A
WARNING.
 
THE AIRCRAFT MEASURED A CENTRAL PRESSURE OF 1010 MB...NOT VERY
LOW...BUT THE PRESSURE GRADIENT TO THE EAST OF THE STORM IS LARGE.
A 15Z SHIP REPORT OF 40 KNOTS ABOUT 80 N MI NORTHEAST OF THE CENTER
...ALONG WITH AIRCRAFT OBSERVATIONS...IS THE BASIS FOR INCREASING
THE WIND SPEED TO 40 KNOTS.  THE SHIPS MODEL BRINGS THE WIND TO 62
KNOTS IN 24 HOURS UNDER LIGHT SHEAR AND WARM SSTS.  IN CONTRAST
NONE OF THE GLOBAL MODELS SHOW STRENGTHENING.  ALSO THE PRESENT
DEEP CONVECTION PATTERN IS NOT VERY IMPRESSIVE.   THE OFFICIAL
FORECAST IS A COMPROMISE 55 KNOTS AT 24 HOURS.
 
FORECASTER LAWRENCE
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      29/2100Z 24.8N  91.1W    40 KT
 12HR VT     30/0600Z 26.4N  91.9W    45 KT
 24HR VT     30/1800Z 28.5N  92.5W    55 KT
 36HR VT     01/0600Z 30.5N  92.0W    30 KT...INLAND
 48HR VT     01/1800Z 31.5N  90.5W    20 KT...INLAND
 72HR VT     02/1800Z 33.0N  86.0W    20 KT...INLAND
 96HR VT     03/1800Z...INLAND
 
 
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