363 
 WTNT44 KNHC 130237
 TCDAT4
 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
  
 $$