581 
 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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