Hurricane IVAN

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HURRICANE IVAN DISCUSSION NUMBER  43
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SUN SEP 12 2004
 
AIR FORCE RECON THIS EVENING FOUND A PEAK FLIGHT-LEVEL...700
MB...WIND OF 155 KT IN THE NORTHWEST EYEWALL OF THE HURRICANE.
THIS OBSERVATION SUPPORTS A CURRENT INTENSITY OF 140 KT...SO IVAN
HAS REGAINED CATEGORY 5 STATUS.  SOME FLUCTUATIONS IN STRENGTH ARE
LIKELY OVER THE NEXT DAY OR SO...AND IF THE EYEWALL PASSES OVER
PORTIONS OF EXTREME WESTERN CUBA A SLIGHT REDUCTION IN INTENSITY
MAY OCCUR.  THE INTENSITY FORECAST FOR IVAN OVER THE GULF OF MEXICO
IS MOST PROBLEMATIC.  DATA FROM THE NOAA G-IV JET SHOW WESTERLY
UPPER-TROPOSPHERIC FLOW OVER THE SOUTHEASTERN GULF OF MEXICO...
WHICH WOULD CAUSE AN INCREASE IN SHEAR OVER IVAN ONCE IT ENTERS THE
GULF.  ALSO...ANALYSES FROM THE UNIVERSITY OF WISCONSIN CIMSS SHOWS
EVEN MORE WESTERLY SHEAR OVER THE NORTHEASTERN GULF OF MEXICO THAN
OVER THE SOUTHEASTERN GULF.  HOWEVER THE GFS MODEL 200 MB WIND
FORECAST SHOWS THE OUTFLOW OF THE HURRICANE DOMINATING THE
CIRCULATION OVER THE EASTERN GULF IN 2-3 DAYS...AND THE LATEST
SHIPS MODEL RUN SHOWS LESS VERTICAL SHEAR AT THIS TIME FRAME THAN
IN EARLIER RUNS.  WE ARE ASSUMING THAT SHEAR WILL PLAY SOME ROLE IN
WEAKENING THE HURRICANE BEFORE LANDFALL.  NONETHELESS IVAN IS
EXPECTED TO BE A POWERFUL AND DANGEROUS HURRICANE WHEN IT REACHES
THE UNITED STATES COAST.
 
THE EYE CONTINUES TO WOBBLE ALONG A GENERALLY WEST-NORTHWESTWARD
HEADING...300/8. THERE IS NOT MUCH CHANGE TO THE TRACK FORECAST
REASONING. A SHORTWAVE TROUGH NEAR THE LOWER MISSISSIPPI RIVER
VALLEY IS ERODING THE RIDGE TO THE NORTH AND NORTHEAST OF IVAN.
THIS SHOULD INDUCE A TURN TO THE NORTHWEST VERY SOON. BY AROUND 48
HOURS...IT IS EXPECTED THAT IVAN WILL BE MOVING NORTHWARD THROUGH
THE WEAKNESS IN THE RIDGE OVER THE EASTERN GULF OF MEXICO. COMPARED
TO YESTERDAY...THERE HAS BEEN INCREASE IN THE DYNAMICAL MODEL
SPREAD BEYOND 48 HOURS. THE OFFICIAL FORECAST IS SHIFTED A LITTLE
MORE TO THE WEST BUT IS EAST OF THE CONSENSUS TRACK...AND LEANS
TOWARD THE GFDL AND GFS SOLUTIONS.

FORECASTER PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      13/0300Z 19.7N  83.2W   140 KT
 12HR VT     13/1200Z 20.8N  84.1W   140 KT
 24HR VT     14/0000Z 22.3N  85.0W   135 KT
 36HR VT     14/1200Z 23.9N  85.9W   135 KT
 48HR VT     15/0000Z 25.8N  86.5W   125 KT
 72HR VT     16/0000Z 30.0N  86.5W   115 KT
 96HR VT     17/0000Z 34.0N  84.5W    45 KT...INLAND
120HR VT     18/0000Z 37.0N  82.0W    20 KT...INLAND
 
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