000 WTNT44 KNHC 042032 TCDAT4 HURRICANE IKE DISCUSSION NUMBER 15 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092008 500 PM EDT THU SEP 04 2008 THERE HAS BEEN LITTLE CHANGE TO THE OVERALL APPEARANCE OF IKE DURING THE PAST FEW HOURS. IKE IS MAINTAINING A WELL-DEFINED EYE...THOUGH CLOUD TOPS HAVE WARMED SOME IN THE EYEWALL RECENTLY. IT IS INTERESTING THAT WHILE IKE STARTED OUT AS A LARGE SYSTEM...THE CLOUD CANOPY HAS NOTICEABLY SHRUNK TODAY WITH FEW OUTER BANDS. THERE HAS BEEN ONLY A SMALL DECREASE IN OBJECTIVE T-NUMBERS...SO THE INITIAL INTENSITY IS REDUCED SLIGHTLY TO 115 KT. STRONG NORTHEASTERLY SHEAR IS LIKELY DURING THE NEXT DAY OR SO...WHICH SHOULD CAUSE WEAKENING. IN FACT...THE SHIPS MODEL RESPONDS TO THE SHEAR BY WEAKENING THIS SYSTEM TO A CATEGORY ONE HURRICANE...THOUGH THE GFDL/HWRF ARE CONSIDERABLY HIGHER. IN A COUPLE DAYS...VERTICAL WIND SHEAR IS FORECAST TO WEAKEN AND...COMBINED WITH RATHER WARM WATER WATERS EAST OF THE BAHAMAS...SHOULD RESULT IN RESTRENGTHENING. THE HURRICANE'S EXACT TRACK IS IMPORTANT BECAUSE IT COULD BE IMPACTED BY COOLER WATERS UPWELLED BY HANNA. THE OFFICIAL FORECAST IS CLOSE TO THE PREVIOUS ONE BUT IS A LITTLE LOWER FOR THE FIRST 36 HOURS OUT OF RESPECT FOR THE SHIPS/LGEM MODELS. IKE IS EXPECTED TO BE A POWERFUL HURRICANE AS IT APPROACHES THE BAHAMAS IN A COUPLE OF DAYS. THE INITIAL MOTION ESTIMATE IS 285/12...SLOWER THAN BEFORE AND A LITTLE TO THE LEFT. RIDGING FROM THE CENTRAL ATLANTIC IS FORECAST TO BUILD TO THE NORTH AND NORTHWEST OF THE TROPICAL CYCLONE... CAUSING A WEST...AND THEN WEST-SOUTHWEST MOTION OF IKE BY LATE TOMORROW. THE STRENGTH OF THE RIDGING BETWEEN IKE AND HANNA WILL BE CRITICAL TO WHEN AN EVENTUAL TURN TOWARD THE WEST-NORTHWEST WILL OCCUR IN THE LONG-RANGE. THERE HAS BEEN A NOTICEABLE WESTWARD SHIFT IN ALMOST ALL OF THE GLOBAL MODEL GUIDANCE TODAY...WITH THE GFDL/ECMWF EVEN TAKING THE SYSTEM AS FAR SOUTHWEST AS CUBA. THE OTHER MODELS ARE PRETTY CLUSTERED ON A TRACK NEAR OR THROUGH THE CENTRAL AND NORTHWESTERN BAHAMAS. THE NHC FORECAST IS SHIFTED WESTWARD AND IS PRETTY CLOSE TO THE HWRF MODEL. ONE SHOULD NOT FOCUS ON THE EXACT 4 AND 5 DAY FORECAST POSITIONS BECAUSE LARGE UNCERTAINTIES EXIST AT THOSE TIMES. FORECAST POSITIONS AND MAX WINDS INITIAL 04/2100Z 23.6N 58.2W 115 KT 12HR VT 05/0600Z 23.9N 60.0W 105 KT 24HR VT 05/1800Z 23.7N 62.5W 95 KT 36HR VT 06/0600Z 23.2N 65.1W 95 KT 48HR VT 06/1800Z 22.7N 67.7W 100 KT 72HR VT 07/1800Z 22.5N 72.5W 105 KT 96HR VT 08/1800Z 24.0N 76.0W 110 KT 120HR VT 09/1800Z 25.5N 79.0W 110 KT $$ FORECASTER BLAKE