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HURRICANE ISAAC DISCUSSION NUMBER  32
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT FRI SEP 29 2000
 
ISAAC CONTINUES TO SHOW SIGNS OF WEAKENING NOW THAT THE CYCLONE IS
UNDERGOING AN EYEWALL REPLACEMENT CYCLE AS SEEN IN INFRARED IMAGERY
AND IN A 29/0207Z TRMM OVERPASS.  HOWEVER...THE OVERALL CONVECTIVE
ORGANIZATION AND OUTFLOW REMAIN GOOD.
 
THE INITIAL MOTION ESTIMATE IS 350/17.  THE WESTERN PORTION OF THE
SUBTROPICAL RIDGE APPEARS TO BE FLATTENING OUT IN WATER VAPOR
IMAGERY AND ISAAC SHOULD BEGIN TO TURN MORE TOWARD THE NORTH WITHIN
THE NEXT 12 HOURS.  RECURVATURE SHOULD OCCUR IN ABOUT 24 HOURS WITH
A GRADUAL ACCELERATION TO THE NORTHEAST AFTERWARDS.  THE LATEST
MODEL GUIDANCE IS NOW TIGHTLY CLUSTERED ALONG THE PREVIOUS TWO
FORECAST TRACKS...SO THE OFFICIAL FORECAST IS JUST AN EXTENSION OF
THE PREVIOUS FORECAST AND IS CLOSE TO THE GFDL SOLUTION.  THE UKMET
MODEL IS NOW IN LINE WITH THE REST OF THE GUIDANCE AND MUCH FASTER
THAN THE PREVIOUS 2 MODEL RUNS.

GRADUAL WEAKENING IS EXPECTED NOW THAT ISAAC IS UNDERGOING AN
EYEWALL REPLACEMENT CYCLE AND MOVING OVER COOLER WATER.  HOWEVER...
AS MENTIONED IN THE PREVIOUS ADVISORY...ONLY GRADUAL SLOW WEAKENING
IS FORECAST THROUGH 36 HOURS DUE TO THE IMPRESSIVE OUTFLOW PATTERN.
AFTERWARDS...MORE RAPID WEAKENING IS EXPECTED AS ISAAC TRACKS OVER
24C TO 22C WATER.

THE 12 FT SEAS RADII WERE INCREASED SIGNIFICANTLY BASED ON 06Z 
SHIP REPORTS.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     29/0900Z 30.5N  56.0W   110 KTS
12HR VT     29/1800Z 32.8N  56.2W   105 KTS
24HR VT     30/0600Z 35.6N  54.6W   100 KTS
36HR VT     30/1800Z 38.0N  52.0W    95 KTS
48HR VT     01/0600Z 40.0N  48.5W    85 KTS
72HR VT     02/0600Z 45.0N  37.5W    70 KTS
 
 
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