ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM HURRICANE HERNAN DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008 800 PM PDT SUN AUG 10 2008 SATELLITE IMAGES INDICATE THAT THE EYE OF HERNAN HAS SHRUNK IN DIAMETER OVER THE PAST FEW HOURS...THOUGH THE EYE HAS ALSO BECOME A LESS WELL-DEFINED. SINCE DVORAK T-NUMBERS HAVE NOT CHANGED...THE INITIAL INTENSITY WILL REMAIN 75 KT. A STEADY DEMISE OVER COLD WATERS FOR HERNAN SEEMS LIKELY FOR THE FORECAST PERIOD. IN ABOUT 24 HOURS...UPPER-LEVEL WINDS ARE FORECAST TO SHIFT FROM LIGHT EASTERLY TO LIGHT WESTERLY...WHICH MAY HASTEN THE WEAKENING OF THE TROPICAL CYCLONE. THE INTENSITY FORECAST IS CLOSE TO A CONSENSUS OF THE LGEM/GFDL MODELS AND THE PREVIOUS FORECAST. ALTHOUGH MOST GUIDANCE SUGGESTS THE SYSTEM WILL REMAIN A TROPICAL CYCLONE FOR THE NEXT 5 DAYS...IT SEEMS UNLIKELY THAT PERSISTENT CONVECTION WILL CONTINUE NEAR HERNAN DUE TO A COMBINATION OF COLD WATERS AND INCREASING SHEAR AT THE END OF THE PERIOD. THUS...THE FORECAST WILL CALL FOR THE SYSTEM TO DISSIPATE AROUND THE TIME IT REACHES THE CENTRAL PACIFIC. THE INITIAL MOTION ESTIMATE IS 285/9...AND THE CYCLONE APPEARS TO BE GRADUALLY TURNING TO THE LEFT DUE TO SUBTROPICAL RIDGING BUILDING TO ITS NORTHWEST. GLOBAL MODELS ARE IN SURPRISINGLY GOOD AGREEMENT ON AN ATYPICAL WEST-SOUTHWESTWARD MOTION BEGINNING IN DAY OR TWO. THE NEW FORECAST TRACK IS JUST A HAIR SOUTH OF THE PREVIOUS FORECAST AND IS PRETTY CLOSE TO THE 12Z ECMWF MODEL NEAR THE MIDDLE OF THE TRACK GUIDANCE ENVELOPE. FORECAST POSITIONS AND MAX WINDS INITIAL 11/0300Z 18.4N 128.4W 75 KT 12HR VT 11/1200Z 18.6N 129.7W 65 KT 24HR VT 12/0000Z 18.5N 131.1W 55 KT 36HR VT 12/1200Z 18.2N 132.5W 45 KT 48HR VT 13/0000Z 17.7N 133.8W 40 KT 72HR VT 14/0000Z 16.5N 136.5W 30 KT 96HR VT 15/0000Z 16.0N 139.5W 25 KT...DISSIPATING 120HR VT 16/0000Z 15.5N 143.5W 20 KT...REMNANT LOW $$ FORECASTER BLAKE NNNN
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