205 
 WTNT44 KNHC 120933
 TCDAT4
 HURRICANE IVAN DISCUSSION NUMBER  40 CORRECTED
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
 5 AM EDT SUN SEP 12 2004
 
 ...CORRECTION...48 AND 72 HOUR POSITIONS ARE OVER WATER....
  
 AN AIR FORCE AIRCRAFT IS CURRENTLY IN THE HURRICANE.  THE LATEST
 CENTRAL PRESSURE IS 918 MB AND THE HIGHEST 700-MB FLIGHT LEVEL WIND
 SPEED IS 140 KT AT A POSTION 12 N MI NORTHEAST OF THE CENTER.  THE
 INITIAL WIND SPEED IS REDUCED TO 135 KT ON THE BASIS OF THE ABOVE.
 THE AIRCRAFT REPORTS A SECONDARY WIND MAXIMUM 27 N MI FROM THE
 CENTER WHICH COULD BE THE START OF ANOTHER EYEWALL REPLACEMENT
 CYCLE.  THEREFORE THE WIND SPEED IS FORECAST TO INCREASE TO 145 KT
 AT 12 AND 24 HOURS.  INCREASING VERTICAL SHEAR IS INDICATED BY THE
 SHIPS MODEL AS IVAN MOVES INTO THE GULF OF MEXICO AND SOME
 WEAKENING IS FORECAST AFTER IVAN MOVES NORTH OF CUBA.
  
 THE INITIAL MOTION ESTIMATE IS 290/8.  THE GUIDANCE IS FAIRLY
 CLOSELY CLUSTERED ABOUT A TURN TOWARD THE NORTHWEST AND THEN NORTH
 OVER THE NEXT FEW DAYS AS IVAN MOVES INTO A WEAKNESS IN THE
 SUBTROPICAL RIDGE WHICH IS FORECAST TO AMPLIFY TO THE EAST OF
 FLORIDA.  THE OFFICIAL TRACK FORECAST IS VERY SIMILAR TO THE
 PREVIOUS ADVISORY AND IS A LITTLE TO THE EAST OF A CONSENSUS OF THE
 GUIDANCE MODELS.
  
 REPEATING THE REMINDER FROM THE PREVIOUS DISCUSSION...BEAR IN MIND
 THAT 3-4 DAY TRACK FORECASTS ARE FAR FROM EXACT...SO THERE IS
 CONSIDERABLE UNCERTAINTY AS TO JUST WHEN AND WHERE IVAN WILL MAKE
 LANDFALL IN THE UNITED STATES.   AND INTENSITY FORECASTS ARE EVEN
 LESS CERTAIN.
  
 FORECASTER LAWRENCE
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      12/0900Z 18.6N  80.8W   135 KT
  12HR VT     12/1800Z 19.2N  81.8W   145 KT
  24HR VT     13/0600Z 20.6N  83.0W   145 KT
  36HR VT     13/1800Z 22.2N  84.1W   140 KT...INLAND
  48HR VT     14/0600Z 23.9N  84.8W   125 KT...OVER WATER
  72HR VT     15/0600Z 27.7N  85.6W   110 KT...OVER WATER
  96HR VT     16/0600Z 32.0N  85.3W    60 KT...INLAND
 120HR VT     17/0600Z 36.5N  82.5W    25 KT...INLAND
  
  
 $$