Hurricane ISABEL

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HURRICANE ISABEL DISCUSSION NUMBER  28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT FRI SEP 12 2003
 
RADAR IMAGES TRANSMITTED FROM A NOAA/HURRICANE RESEARCH DIVISION
FLIGHT INTO ISABEL LATE THIS AFTERNOON SHOWED THE DEVELOPMENT OF A
SECOND CONCENTRIC EYEWALL ABOUT 20 NM OUTSIDE OF THE INNER EYEWALL.
THE AIRCRAFT CREW ALSO REPORTED A STEPPED FREQUENCY MICROWAVE
RADIOMETER MEASUREMENT OF A 140 KT SURFACE WIND LATE IN THE
AFTERNOON. CONCURRENT WITH THIS RE-DEVELOPMENT OF AN OUTER
EYEWALL...THE CORE CONVECTION IS CURRENTLY WEAKENING AS IT DID LAST
NIGHT AT THIS TIME. IN ADDITION...MICROWAVE IMAGERY INDICATES THAT
SOME DRY AIR HAS BEEN INFILTRATING THE CIRCULATION. SUBJECTIVE
DVORAK T-NUMBERS ARE DOWN TO 6.0...AND THE LATEST CIMSS ADVANCED
OBJECTIVE DVORAK 3-HR AVERAGE T NUMBER IS ALSO 6.0...WELL BELOW
CATEGORY FIVE INTENSITY. I VERY MUCH DOUBT THAT ISABEL STILL HAS
WINDS OF 140 KT...BUT SINCE ANOTHER AIRCRAFT WILL BE IN THE
HURRICANE IN JUST THREE HOURS...WE WILL WAIT FOR CONFIRMATION OF
THIS APPARENT WEAKENING TREND. IT IS VIRTUALLY UNHEARD OF FOR A
HURRICANE TO REMAIN AT CATEGORY FIVE STRENGTH FOR MORE THAN 30
HOURS. HOWEVER...ISABEL IS EXPECTED TO REMAIN A MAJOR HURRICANE
THROUGHOUT THE FORECAST PERIOD.
 
THE INITIAL MOTION IS 275/8.  ISABEL REMAINS SOUTH OF A DEEP-LAYER
ANTICYCLONE THAT IS PROVIDING THE WESTWARD STEERING CURRENT.  THIS
ANTICYCLONE CONTINUES WESTWARD IN STEP WITH THE HURRICANE...AND
MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON A WEST TO
WEST-NORTHWEST TRACK FOR THE NEXT 72 HOURS.  BY 72 HOURS...THE
EVOLUTION OF A MID- TO UPPER-LEVEL LOW CURRENTLY OVER THE CAROLINAS
COULD PLAY A KEY ROLE IN WHAT PORTION OF THE U.S. EAST COAST WOULD
EVENTUALLY BE AFFECTED BY ISABEL.  THE GFS AND NOGAPS MODELS ARE
VERY SIMILAR IN HOLDING THIS FEATURE IN PLACE ALMOST A DAY LONGER
THAN THE UKMET...WITH THE RESULT THAT THE FORMER TWO MODELS TURN
ISABEL MUCH MORE SHARPLY NORTHWARD THAN THE UKMET.  THE GFDL TURNS
ISABEL EVEN MORE SHARPLY THAN THE GFS AND NOGAPS MODELS...AND THE
EUROPEAN MODEL ALSO SEEMS TO FAVOR AN EARLIER TURN NORTH.  THE
OFFICIAL FORECAST HAS BEEN BEEN SHIFTED TO THE RIGHT OF THE
PREVIOUS ADVISORY TRACK...BUT IS STILL CLOSER TO THE UKMET THAN THE
OTHER GUIDANCE.  IN PART THIS IS TO MAINTAIN CONTINUITY WITH
PREVIOUS FORECASTS...BUT ALSO BECAUSE THE UKMET HAS BEEN PRESENTING
A MORE CONSISTENT SOLUTION OVER THE PAST COUPLE OF DAYS THAN HAVE
THE OTHER MODELS.  

FORECASTER FRANKLIN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      13/0300Z 21.8N  59.5W   140 KT
 12HR VT     13/1200Z 22.2N  60.9W   135 KT
 24HR VT     14/0000Z 22.8N  63.0W   130 KT
 36HR VT     14/1200Z 23.4N  65.1W   130 KT
 48HR VT     15/0000Z 24.0N  67.0W   130 KT
 72HR VT     16/0000Z 25.0N  70.0W   125 KT
 96HR VT     17/0000Z 27.0N  72.5W   115 KT
120HR VT     18/0000Z 29.5N  74.5W   105 KT
 
 
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