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| #7987 (Received by flhurricane at: 4:50 AM 12.Sep.2004) TCDAT4 HURRICANE IVAN DISCUSSION NUMBER 40 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT SUN SEP 12 2004 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...INLAND 72HR VT 15/0600Z 27.7N 85.6W 110 KT...OVER WATER 96HR VT 16/0600Z 32.0N 85.3W 60 KT...OVER WATER 120HR VT 17/0600Z 36.5N 82.5W 25 KT...INLAND |
