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HURRICANE ISIDORE DISCUSSION NUMBER  22
NATIONAL WEATHER SERVICE MIAMI FL
11 AM EDT SAT SEP 21 2002
 
AIR FORCE RESERVE HURRICANE HUNTER INFORMATION INDICATES HURRICANE
ISIDORE HAS CONTINUED TO STRENGTHEN AND IS NOW A MAJOR HURRICANE
...CATEGORY 3...BASED ON AN EYEWALL DROPSONDE WIND REPORT OF 100 KT
AT 21/1200Z. THIS INTENSITY IS ALSO SUPPORTED BY A CONSENSUS DVORAK 
SATELLITE INTENSITY ESTIMATE OF T5.5...OR 102 KT...FROM ALL THREE 
SATELLITE AGENCIES.
 
THE INITIAL MOTION ESTIMATE IS 270/6.  RECON FIX POSITONS SINCE
ABOUT 06Z INDICATE ISIDORE HAS ACTUALLY MOVED WEST-SOUTHWESTWARD 
DURING THE PAST 6 HOURS...BUT THIS APPEARS TO BE A TEMPORARY MOTION 
CAUSED BY SOME BINARY INTERACTION WITH A MID- TO UPPER-LEVEL LOW 
OVER THE BAY OF CAMPECHE. ISIDORE IS EXPECTED TO RESUME A WESTWARD 
MOTION SHORTLY AS THE BAY OF CAMPECHE LOW DROPS FARTHER SOUTH 
WEAKENS AND ACTS TO STEER THE HURRICANE MORE WESTWARD...POSSIBLY 
KEEPING THE EYE JUST NORTH OF THE YUCATAN PENINSULA. SO MUCH FOR THE 
SHORT TERM MOTION. THE LONGER TERM TRACK FORECAST IS NOT AS 
STRAIGHT-FORWARD. MOST OF THE NHC MODEL GUIDANCE TAKES ISIDORE 
WESTWARD THROUGHOUT THE FORECAST PERIOD...EXCEPT FOR THE NOGAPS AND 
AVN MODELS WHICH GRADUALLY TURN THE CYCLONE WEST-NORTHWESTWARD AFTER 
48 HOURS. A RATHER VIGOROUS SHORTWAVE TROUGH OVER THE PACIFIC 
NORTHWEST IS EXPECTED TO DROP INTO THE BASE OF THE MEAN LONGWAVE 
TROUGH CURRENTLY OVER THE CENTRAL U.S. THE 00Z MODELS DID NOT 
INITIALIZE THE SHORTWAVE TROUGH VERY WELL AT 00Z...SO I AM NOT GOING 
TO MAKE ANY SIGNIFICANT CHANGES TO PREVIOUS FORECAST TRACK GIVEN THE 
CURRENT WEAK STEERING CURRENTS THAT MAY BECOME EVEN WEAKER WITH 
TIME. THE OFFICIAL TRACK IS JUST SLIGHTLY SOUTH OF THE PREVIOUS 
TRACK THROUGH 36 HOURS AND THEN BACK ON TRACK AFTER THAT. THIS IS 
CONSISTENT WITH THE AVN...AVN ENSEMBLE AND NOGAPS MODELS.

THE CENTRAL PRESSURE DROPPED 10 MB IN 6 HOURS BETWEEN 06Z AND 
12Z...SUGGESTING THAT ISIDORE IS LIKELY UNDERGOING A PERIOD OF RAPID 
INTENSIFICATION. THIS TREND SHOULD CONTINUE FOR ANOTHER 12 HOUR OR 
SO BEFORE THE HURRICANE BEGINS TO INTERACT WITH THE YUCATAN 
PENINSULA. THE CENTER IS FORECAST TO REMAIN OFFSHORE...SO SOME SLOW 
STRENGTHENING IS POSSIBLE THROUGHOUT THE PERIOD. THE UPPER-LEVEL 
ENVIRONMENT FAVORS AN EXCELLENT OUTFLOW PATTERN TO PERSIST...BUT 
UPPER-LEVEL WESTERLY WINDS AT MERIDA THIS MORNING SUGGEST THAT SOME 
SHEAR AND DRY AIR INTRUSION MAY UNDERCUT THE OTHERWISE FAVORABLE 
UPPER-LEVEL OUTFLOW REGIME. FOR THIS REASON...I DID NOT TAKE ISIDORE 
UP TO 115 KT IN 12 HOURS...BUT THAT IS STILL A POSSIBILITY. THE 
SHIPS INTENSITY MODEL FORECAST WAS FOLLOWED CLOSELY AND IT BRINGS 
ISIDORE UP 127 KT IN 48 HOURS AND 128 KT IN 60 HOURS...WHICH SEEMS 
REASONABLE GIVEN THAT THE SSTS AHEAD OF THE CYCLONE INCREASE FROM 
84F TO 86F.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     21/1500Z 21.9N  86.1W   100 KTS
12HR VT     22/0000Z 21.9N  86.9W   110 KTS
24HR VT     22/1200Z 21.9N  88.0W   115 KTS
36HR VT     23/0000Z 21.9N  89.2W   115 KTS
48HR VT     23/1200Z 22.0N  90.5W   120 KTS
72HR VT     24/1200Z 22.5N  92.5W   125 KTS
 
 
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