[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 120841
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


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