000 WTPZ44 KNHC 092034 TCDEP4 HURRICANE HERNAN DISCUSSION NUMBER 13 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008 200 PM PDT SAT AUG 09 2008 VISIBLE SATELLITE IMAGERY CONTINUES TO DEPICT A WELL-DEFINED EYE... BUT INFRARED IMAGERY INDICATES THAT THE CLOUD TOPS SURROUNDING THE EYE HAVE WARMED A LITTLE THIS AFTERNOON. OBJECTIVE DVORAK T-NUMBERS FROM UW-CIMSS APPEAR TO HAVE PEAKED AROUND T6.2 LATE THIS MORNING. A BLEND OF THE SUBJECTIVE AND OBJECTIVE DVORAK ESTIMATES SUGGEST THAT HERNAN'S PEAK INTENSITY COULD HAVE BEEN AROUND 110 KT. THE LATEST SUBJECTIVE INTENSITY ESTIMATES FROM TAFB AND SAB ARE 102 KT. SINCE THE RAW OBJECTIVE T-NUMBERS HAVE DECREASED THE INITIAL INTENSITY REMAINS 105 KT. VERTICAL SHEAR IS FORECAST TO REMAIN LOW DURING THE NEXT SEVERAL DAYS SO COOLER SSTS ALONG THE FORECAST TRACK AND A MORE STABLE ENVIRONMENT WILL DETERMINE HOW FAST HERNAN WEAKENS. THE HURRICANE IS EXPECTED TO MOVE OVER THE 26 DEGREE CELSIUS ISOTHERM IN ABOUT 12 HOURS SO WEAKENING SHOULD BEGIN SOON. THERE IS A LARGE SPREAD IN GUIDANCE AS TO HOW FAST HERNAN WILL SPIN DOWN...IN FACT...THE HWRF MODEL KEEPS HERNAN AS A FORMIDABLE TROPICAL STORM THROUGH THE FORECAST PERIOD. THE NEW INTENSITY PREDICTION SHOWS A LITTLE MORE WEAKENING DURING THE FIRST 48 HOURS OF THE FORECAST THAN THE PREVIOUS ADVISORY INDICATED...BUT IT IS CLOSE TO THE PREVIOUS FORECAST AND THE LGEM MODEL THEREAFTER. THE HURRICANE IS MOVING WEST-NORTHWESTWARD OR 300 DEGREES AT 9 KT. THE MODELS ARE IN GOOD AGREEMENT ON A WEST-NORTHWESTWARD HEADING WITH SOME DECREASE IN FORWARD SPEED DURING THE 12-24 HOURS. BEYOND 24 HOURS...THE MODELS PREDICT A MORE WESTWARD TRACK FOR A COUPLE OF DAYS....FOLLOWED BY A WEST-SOUTHWEST TURN AS THE CYCLONE BECOMES A SHALLOWER SYSTEM. THE NEW FORECAST IS A LITTLE SLOWER AND SLIGHTLY NORTH OF THE PREVIOUS TRACK THROUGH 36 HOURS...BUT IS NEARLY IDENTICAL THEREAFTER. FORECAST POSITIONS AND MAX WINDS INITIAL 09/2100Z 16.2N 124.0W 105 KT 12HR VT 10/0600Z 16.8N 125.2W 100 KT 24HR VT 10/1800Z 17.4N 126.7W 85 KT 36HR VT 11/0600Z 17.7N 128.0W 70 KT 48HR VT 11/1800Z 17.8N 129.3W 60 KT 72HR VT 12/1800Z 17.8N 131.5W 45 KT 96HR VT 13/1800Z 17.5N 133.5W 35 KT 120HR VT 14/1800Z 16.5N 136.5W 30 KT $$ FORECASTER BROWN