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TROPICAL STORM ISIDORE DISCUSSION NUMBER  11
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT WED SEP 18 2002
 
ALTHOUGH THE HURRICANE HUNTER AIRCRAFT DID NOT SEND A VORTEX 
MESSAGE...HIGH-DENSITY OBSERVATIONS FROM THE AIRCRAFT INDICATE THAT 
THE CENTER OF ISIDORE HAS REFORMED NORTH OF THE PREVIOUS FIX 
LOCATION...ROUGHLY WHERE THE DEEPEST CONVECTION WAS OCCURRING 
EARLIER THIS AFTERNOON.  THE PEAK FLIGHT-LEVEL WIND WAS 59 KT...AND 
IS THE BASIS FOR THE ADVISORY INTENSITY OF 50 KT.  MOMENTS AGO...THE 
AIRCRAFT CONFIRMED THE NORTHERN CENTER WITH A NEW PRESSURE OF 999 
MB.

THE INITIAL MOTION IS NOW UNCERTAIN...SINCE I DO NOT KNOW HOW MUCH 
OF THE APPARENT TRANSLATION IS MOTION AND HOW MUCH IS REFORMATION.  
MY ESTIMATE IS 325/8.  I NOTE THAT THE 12Z AVN DID HAVE A SHORT TERM 
NORTHWARD JOG PRETTY MUCH IN LINE WITH WHAT IS HAPPENING.  THE 
RELOCATION HAS FORCED AN ADJUSTMENT IN THE EARLY PART OF THE 
FORECAST TRACK...BUT THE OVERALL THINKING IS UNCHANGED.  GUIDANCE IS 
IN GOOD AGREEMENT ON A NORTHWESTWARD TRACK FOR THE NEXT 48 TO 72 
HOURS...WITH A DECREASE IN FORWARD SPEED NEAR THE END OF THE 
FORECAST PERIOD.

THERE IS AMPLE HEAT ENERGY BELOW...THE UPPER-LEVEL OUTFLOW PATTERN 
LOOKS GOOD...AND WITH A MORE SOLID INNER CORE CIRCULATION 
FORMING...ISIDORE SHOULD CONTINUE TO STRENGTHEN...ALTHOUGH THE NEW 
TRACK IS CLOSER TO THE CUBAN COAST...AND THIS MIGHT BE A SLIGHT 
INHIBITING FACTOR.   
 
IT NOW APPEARS THAT THE MID- TO UPPER-LEVEL TROUGH CURRENTLY MOVING
THROUGH THE CENTRAL U.S. WILL BYPASS ISIDORE...AND THIS LESSENS THE
THREAT TO SOUTH AND CENTRAL FLORIDA.  GLOBAL MODELS CUTOFF ANOTHER
MID-LEVEL LOW NEAR BERMUDA AND TAKE IT SOUTHWESTWARD BETWEEN BERMUDA
AND THE BAHAMAS NEAR THE END OF THE FORECAST PERIOD.  THE NORTHERLY
FLOW ON THE BACK SIDE OF THIS LOW HELPS TO LEAVE ISIDORE IN A WEAK
STEERING ENVIRONMENT IN THE SOUTHERN GULF OF MEXICO.  SPECULATING A
BIT BEYOND THREE DAYS...THERE IS APPARENTLY ENOUGH MODEL RIDGING IN
THE NORTHERN GULF FOR THE UKMET AND AVN TO TAKE ISIDORE SLOWLY
WESTWARD.  HOWEVER...IF ISIDORE BECOMES A LARGE AND POWERFUL
HURRICANE...THE ATLANTIC CUTOFF MAY NOT BE AS STRONG OR AS FAR WEST
AS THE MODELS INDICATE...AND THIS COULD MEAN A MORE NORTHERLY...
RATHERLY THAN WESTERLY DRIFT ACROSS THE GULF.
 
 
FORECASTER FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     18/2100Z 19.0N  78.8W    50 KTS
12HR VT     19/0600Z 20.3N  79.6W    55 KTS
24HR VT     19/1800Z 21.3N  81.1W    60 KTS
36HR VT     20/0600Z 22.4N  82.7W    70 KTS
48HR VT     20/1800Z 23.3N  84.0W    75 KTS
72HR VT     21/1800Z 24.0N  85.0W    85 KTS
 
 
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