[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 121434
TCDAT4
HURRICANE IVAN DISCUSSION NUMBER  41
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT SUN SEP 12 2004

THE INITIAL MOTION ESTIMATE IS 300/8.  IVAN HAS REMAINED ON TRACK...
SO THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR
REASONING. THE LATEST 12Z UPPER-AIR DATA INDICATE A SHARP SHORTWAVE
TROUGH OVER THE LOWER MISSISSIPPI VALLEY HAS PUSHED SOUTHEASTWARD
INTO THE CENTRAL GULF OF MEXICO AND HAS ERODED THE RIDGE FROM 500
MB THROUGH THE 300 MB LEVEL. NHC MODEL GUIDANCE IS IN REASONABLE
AGREEMENT ON A GRADUAL TURN TO THE NORTHWEST IN 12 TO 24 HOURS...
WITH A TURN TO THE NORTH AFTER 36 HOURS WHEN IVAN IS EXPECTED TO
EMERGE OVER THE GULF OF MEXICO NORTH OF WESTERN CUBA. THE OFFICIAL
FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS TRACK AND REMAINS
IN THE EASTERN PORTION OF THE NHC MODEL GUIDANCE SUITE.

THERE IS NO CHANGE TO THE CURRENT INTENSITY BASED ON RECENT AIR
FORCE AND NOAA RECON REPORTS. THEREFORE...THERE ALSO REMAINS NO
CHANGE TO THE PREVIOUS INTENSITY FORECAST TREND. IVAN REMAINS WELL
ORGANIZED AND THE OUTFLOW HAS IMPROVED TO THE NORTHWEST. THERE WILL
BE PERIODIC FLUCTUATIONS IN THE INTENSITY DUE TO EYEWALL
REPLACEMENT CYCLES...LIKE THE ONE IVAN IS CURRENTLY GOING
THROUGH...BUT LOW SHEAR AND VERY WARM SSTS AHEAD OF THE HURRICANE
SHOULD AT LEAST KEEP IVAN A CATEGORY FOUR HURRICANE UNTIL EXPECTED
LANDFALL OCCURS OVER WESTERN CUBA IN ABOUT 24 HOURS OR SO.

BECAUSE STEERING ARE CURRENTLY WEAK AND MAY WEAKEN EVEN MORE...THERE
REMAINS CONSIDERABLE UNCERTAINTY AS TO JUST WHEN AND WHERE...AND AT
WHAT INTENSITY...IVAN WILL MAKE LANDFALL IN THE UNITED STATES IN
THE LONGER TIME PERIODS.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      12/1500Z 19.0N  81.5W   135 KT
 12HR VT     13/0000Z 19.8N  82.4W   145 KT
 24HR VT     13/1200Z 21.3N  83.5W   145 KT
 36HR VT     14/0000Z 22.9N  84.4W   140 KT
 48HR VT     14/1200Z 24.7N  85.0W   125 KT
 72HR VT     15/1200Z 28.3N  85.5W   110 KT
 96HR VT     16/1200Z 32.5N  84.5W    55 KT...INLAND
120HR VT     17/1200Z 37.0N  81.5W    25 KT...INLAND


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