[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT44 KNHC 071455
TCDAT4
HURRICANE IVAN DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT TUE SEP 07 2004

LATEST INFORMATION FROM THE RECONNAISSANCE PLANE EARLIER THIS
MORNING INDICATED THAT THE MINIMUM PRESSURE WAS 963 MB AND THE PEAK
WIND AT FLIGHT LEVEL WAS 116 KNOTS. INITIAL INTENSITY HAS BEEN
INCREASED TO 100 KNOTS. THIS IS ALSO SUPPORTED BY SATELLITE
INTENSITY ESTIMATES OF 102 KNOTS FROM FROM BOTH TAFB AND SAB.
CURRENTLY...THE OUTFLOW IS FAIR IN ALL QUADRANTS BUT A LARGE-UPPER
LOW IN CENTRAL CARIBBEAN MAY INDUCE SOME SHEAR OVER THE HURRICANE.
THIS IS ALSO INDICATED BY ANALYSES FROM THE UNIVERSITY OF WISCONSIN
THAT SHOWS A 20-KNOT SOUTHERLY SHEAR AHEAD OF THE HURRICANE...WHICH
COULD HALT INTENSIFICATION IN THE SHORT TERM. HOWEVER...MOST OF THE
GLOBAL MODELS ULTIMATELY MOVE THE UPPER-LOW WESTWARD LEAVING A MORE
FAVORABLE UPPER-LEVEL ENVIRONMENT FOR THE HURRICANE TO STRENGTHEN
AS INDICATED IN THE OFFICIAL FORECAST. IVAN IS A POWERFUL HURRICANE
WHICH IS FORECAST TO BE IN THE NORTHWESTERN CARIBBEAN IN FIVE DAYS.

IVAN IS MOVING TOWARD THE WEST OR 280 DEGREES AT 16 KNOTS. THE
HURRICANE IS SOUTH A RATHER STRONG SUBTROPICAL RIDGE WHICH IS
STEERING THE HURRICANE WESTWARD. IN TIME...A LARGE MID TO UPPER
LEVEL TROUGH IS EXPECTED TO DEVELOP OVER THE CENTRAL UNITED STATES
AND THE GULF OF MEXICO. THIS TROUGH IS FORECAST TO ERODE THE RIDGE
ALLOWING THE HURRICANE TO MOVE MORE TOWARD THE WEST-NORTHWEST AND
NORTHWEST WITH A DECREASE IN FORWARD SPEED BY THE END OF THE
FORECAST PERIOD.  HOW FAR NORTH THE HURRICANE WILL MOVE DEPENDS ON
THE INTENSITY OF TROUGH OVER THE GULF OF MEXICO...AND THIS VARIES
WITH MODELS. THE OFFICIAL FORECAST HAS BEEN SHIFTED SOUTHWARD A
LITTLE BIT AT THE END OF THE FORECAST PERIOD...TO BE IN BETTER
AGREEMENT WITH THE GFDL AND THE FSU SUPERENSEMBLE.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL      07/1500Z 11.8N  60.2W   100 KT
 12HR VT     08/0000Z 12.3N  62.5W   105 KT
 24HR VT     08/1200Z 13.0N  65.6W   110 KT
 36HR VT     09/0000Z 14.0N  68.5W   115 KT
 48HR VT     09/1200Z 15.0N  71.5W   120 KT
 72HR VT     10/1200Z 17.5N  76.0W   120 KT
 96HR VT     11/1200Z 19.5N  80.0W   120 KT
120HR VT     12/1200Z 22.0N  83.0W   120 KT


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