000
WTNT44 KNHC 060904
TCDAT4
HURRICANE IKE DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL092008
500 AM EDT SAT SEP 06 2008

AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT RECORDED A MAXIMUM FLIGHT
LEVEL WIND OF 104 KT OVER THE NORTHWEST QUADRANT AND AN SFMR PEAK
WIND OF 96 KT OVER THE NORTHEASTERN PORTION OF THE CYCLONE. BASED
ON THESE DATA...THE INITIAL INTENSITY IS HELD AT 100 KT. THE
AIRCRAFT METEOROLOGIST ALSO INDICATED THAT IKE HAS A CLOSED 24 NM
DIAMETER EYE. A DROPSONDE WITHIN THE EYE MEASURED 983 MB BUT THAT
WAS WITH A SURFACE WIND OF 16 KT. AS A COMPROMISE...THE CENTRAL
PRESSURE IS ADJUSTED SLIGHTLY TO 982 MB. ALTHOUGH NORTHERLY SHEAR
SEEMS TO BE PERSISTING OVER THE CYCLONE...IT DOES NOT APPEAR TO BE
AFFECTING THE INNER CORE CONVECTION AS MUCH AS IT WAS PREVIOUSLY.
INTENSITY MODELS CONTINUE TO INDICATE THAT THE SHEAR WILL DECREASE
IN ABOUT 24 HOURS...WHICH SHOULD ALLOW FOR SOME STRENGTHENING
BEFORE IKE MOVES NEAR OR OVER THE NORTHERN COAST OF CUBA. THE
INTENSITY FORECAST IS VERY SIMILAR TO THE PREVIOUS PACKAGE BUT NOW
DEPICTS SOME WEAKENING AS IKE TRAVERSES THE CUBAN COAST. OF
COURSE...ANY SLIGHT DEVIATION NORTH OR SOUTH OF THE FORECAST WILL
EITHER ALLOW FOR STRENGTHENING OVER WATER OR A LONGER PERIOD OF
WEAKENING OVER LAND.  LATER ON...CONDITIONS APPEAR RATHER CONDUCIVE
FOR STRENGTHENING OVER THE GULF OF MEXICO.
 
INITIAL MOTION IS ESTIMATED AT 255/14...WITHIN THE DEEP-LAYER FLOW
OF A STRONG RIDGE DIGGING SOUTHWESTWARD OVER THE BAHAMAS...THROUGH
THE STRAITS OF FLORIDA...AND INTO THE SOUTHEASTERN GULF OF MEXICO.
DYNAMICAL MODELS SUGGEST THAT THE RIDGE WILL SHIFT TO A MORE ZONAL
PATTERN DURING THE NEXT 24 TO 36 HOURS WHICH WILL CAUSE IKE TO MOVE
IN A MORE WESTWARD FASHION.  AFTERWARD...GUIDANCE INDICATES THAT
THE SOUTHWEST RIDGE EXTENSION OVER THE SOUTHEASTERN GULF/STRAITS OF
FLORIDA WILL ERODE JUST ENOUGH TO INDUCE A GRADUAL TURN TOWARD THE
NORTHWEST BY THE END OF THE FORECAST PERIOD.  THERE IS MUCH
UNCERTAINTY IN THE MODELS AS TO HOW CLOSE IKE WILL APPROACH THE
NORTHERN COAST OF CUBA.  IN FACT...THE TWO HURRICANE MODELS
ACTUALLY BRING THE CYCLONE OVER THE ISLAND IN 36 HOURS.  WITHOUT
QUESTION...THE PARTICULAR TRACK THAT THE GFDL AND HWRF ARE
SUGGESTING COULD HAVE A SIGNIFICANT IMPACT ON IKE'S INTENSITY.
THE OFFICIAL FORECAST IS WEIGHED HEAVILY ON THE MODEL CONSENSUS AND
IS ADJUSTED JUST TO THE LEFT OF THE PREVIOUS ADVISORY TO COMPENSATE
FOR THE WESTWARD-SHIFTING MODEL TREND.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      06/0900Z 22.4N  67.1W   100 KT
 12HR VT     06/1800Z 22.1N  69.0W   100 KT
 24HR VT     07/0600Z 21.8N  71.6W   100 KT
 36HR VT     07/1800Z 21.6N  74.1W   105 KT
 48HR VT     08/0600Z 21.8N  76.6W   115 KT
 72HR VT     09/0600Z 23.0N  80.5W    90 KT...NEAR COAST OF CUBA
 96HR VT     10/0600Z 24.5N  83.5W   105 KT
120HR VT     11/0600Z 26.0N  85.5W   110 KT
 
$$
FORECASTER ROBERTS/KNABB