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HURRICANE ISIDORE DISCUSSION NUMBER  15
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT THU SEP 19 2002
 
AN AIR FORCE HURRICANE HUNTER AIRCRAFT FOUND THAT THE MINIMUM
PRESSURE IN ISIDORE HAS FALLEN TO 984 MB...AND THE PEAK FLIGHT-LEVEL
WINDS WERE 76 KT.  THE CREW ALSO ESTIMATED SURFACE WINDS OF 70 KT.
ON THIS BASIS...THE ADVISORY WINDS ARE INCREASED TO 65 KT...MAKING
ISIDORE THE SECOND HURRICANE OF THE SEASON.  
 
ISIDORE HAS BEEN BASICALLY ON TRACK TODAY...AND THE INITIAL MOTION
IS 300/8.  THE SHORT-TERM FORECAST IS UNCHANGED...TAKING ISIDORE 
OVER WESTERN CUBA IN 24 HOURS.  IN SPITE OF COPIOUS QUANTITIES OF 
DROPSONDES HAVING BEEN RELEASED IN THE ENVIRONMENT OF ISIDORE FROM 
THE NOAA GULFSTREAM-IV JET OVER THE PAST TWO DAYS...THERE REMAINS 
CONSIDERABLE DIVERGENCE AMONG THE TRACK GUIDANCE MODELS BEYOND 48 
HOURS.  MUCH OF THIS DIVERGENCE APPEARS TO BE RELATED TO THE 
FORECAST DEVELOPMENT OF A CUTOFF MID- TO UPPER-LEVEL LOW BETWEEN 
BERMUDA AND THE BAHAMAS.  THE AVN HAS THE STRONGEST AND MOST 
WESTWARD VERSION OF THIS LOW...AND THE NORTHEASTERLY FLOW AROUND THE 
LOW MAY BE WHY THIS MODEL DRIVES ISIDORE SO STRONGLY SOUTHWESTWARD 
NEAR THE END OF THE FORECAST PERIOD.  FOR WHATEVER REASON...THE AVN 
ENSEMBLE MEAN DOES NOT TAKE ISIDORE AS FAR TO THE WEST AS THE AVN 
CONTROL.  THE UKMET HAS FLIPPED FROM ITS EARLIER NORTHWARD 
TRACK...AND IS NOW IN BETTER AGREEMENT WITH THE AVN.  I REMAIN 
UNCONVINCED THAT THIS LOW WILL BE AS STRONG OR AS WEST AS THE AVN IS 
FORECASTING.  HOWEVER...GIVEN THE OVERALL TENDENCY FOR THE GUIDANCE 
TO SHIFT WESTWARD...I HAVE NUDGED THE OFFICIAL FORECAST WESTWARD 
NEAR 72 HOURS.  THE BOTTOM LINE IS THAT WHEN ISIDORE GETS INTO THE 
GULF...STEERING CURRENTS WILL BECOME VERY WEAK...AND IT WILL LIKELY 
MEANDER AND CAUSE MUCH ANXIETY FOR SEVERAL DAYS. 
 
NOW THAT ISIDORE HAS A WELL-FORMED CORE...THE PACE OF 
INTENSIFICATION SHOULD INCREASE.  THE OUTFLOW PATTERN IS WELL 
ESTABLISHED AND THE SIZE OF THE CYCLONE IS GROWING.  FOUR OUT OF 
FIVE OF THE SHIPS RAPID INTENSIFICATION PREDICTORS ARE POSITIVE.  
THE ONLY SLIGHT NEGATIVE FACTOR OVER THE NEXT 36 HOURS WILL BE 
INTERACTION WITH THE CUBAN LANDMASS.  IT IS LIKELY THAT ISIDORE WILL 
BE A MAJOR HURRICANE IN THE SOUTHEASTERN GULF OF MEXICO.
 
FORECASTER FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     19/2100Z 20.6N  82.0W    65 KTS
12HR VT     20/0600Z 21.3N  83.1W    80 KTS
24HR VT     20/1800Z 22.4N  84.2W    85 KTS
36HR VT     21/0600Z 23.2N  85.0W    90 KTS
48HR VT     21/1800Z 23.5N  85.5W   100 KTS
72HR VT     22/1800Z 24.0N  86.5W   105 KTS
 
 
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