000 WTPZ44 KNHC 090253 TCDEP4 HURRICANE HERNAN DISCUSSION NUMBER 10 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008 800 PM PDT FRI AUG 08 2008 HERNAN NOW HAS A PERSISTENT CLOUD-FILLED EYE EMBEDDED IN A WELL-DEFINED CENTRAL DENSE OVERCAST...WITH MICROWAVE IMAGERY INDICATING THE EYE IS ABOUT 25 N MI WIDE. AT 00Z...SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB WERE 77 KT. SINCE THAT TIME...THE EYE HAS BECOME BETTER DEFINED AND THE AREA OF COLD CLOUD TOPS AROUND IT HAS EXPANDED. BASED ON THIS...THE INITIAL INTENSITY IS INCREASED TO 80 KT. THE CIRRUS OUTFLOW IS GOOD TO EXCELLENT IN THE WESTERN SEMICIRCLE AND POOR TO NONE ELSEWHERE. HERNAN HAS TURNED TO THE RIGHT DURING THE PAST FEW HOURS AND THE INITIAL MOTION IS NOW 285/10. WATER VAPOR IMAGERY CONTINUES TO SHOW A LARGE MID/UPPER-LEVEL TROUGH OVER THE AREA NORTH OF 20N BETWEEN 130-145W...AND WHAT APPEARS TO BE A SMALL MID/UPPER-LEVEL ANTICYCLONE NEAR 21N 121W. THE LATTER FEATURE REMAINS POORLY- RESOLVED IN THE LATEST LARGE-SCALE MODEL RUNS...WHICH AGAIN TURN HERNAN MORE TO THE RIGHT THAN WHAT HAS ACTUALLY OCCURRED. BASED ON THIS AND CURRENT TRENDS...THE FIRST 48 HR OF THE TRACK FORECAST IS NUDGED TO THE NORTH OF THE PREVIOUS FORECAST...BUT STILL LIES ALONG THE LEFT EDGE OF THE MODEL ENVELOPE. AFTER 48 HR...THE TROUGH WEAKENS AND A WEAK MID-LEVEL RIDGE DEVELOPS TO THE NORTH AND NORTHWEST OF HERNAN. THE TRACK GUIDANCE MODELS ARE IN GOOD AGREEMENT ON THIS...FORECASTING THE CYCLONE TO TURN WESTWARD BY 72 HR AND WEST-SOUTHWESTWARD BY 120 HR. THE OFFICIAL FORECAST WILL FOLLOW THIS SCENARIO...WITH THE 72-120 HR PART OF THE TRACK MORE OF LESS IN THE MIDDLE OF THE GUIDANCE ENVELOPE. HERNAN IS MOVING OVER COOLER SEA SURFACE TEMPERATURES AND SHOULD REACH THE 26C ISOTHERM IN ABOUT 36 HR. WHILE SOME ADDITIONAL STRENGTHENING IS POSSIBLE TONIGHT...HERNAN SHOULD START TO WEAKEN IN 24-36 HR EVEN THOUGH THE EASTERLY SHEAR THAT HAS HAMPERED THE SYSTEM IS FORECAST TO DIMINISH. THE NEW INTENSITY FORECAST IS AN UPDATE OF THE PREVIOUS FORECAST...CALLING FOR HERNAN TO REACH A PEAK INTENSITY OF 85 KT IN ABOUT 12 HR...WEAKEN TO A TROPICAL STORM IN ABOUT 48 HR...AND WEAKEN TO A TROPICAL DEPRESSION IN ABOUT 120 HR. THE INTENSITY FORECAST IS A BIT ABOVE THE MODEL GUIDANCE FOR THE FIRST 36 HR...AND IN GOOD AGREEMENT WITH THE GFDL AND FLORIDA STATE SUPERENSEMBLE FROM 96-120 HR. FORECAST POSITIONS AND MAX WINDS INITIAL 09/0300Z 15.1N 121.7W 80 KT 12HR VT 09/1200Z 15.4N 123.0W 85 KT 24HR VT 10/0000Z 16.0N 124.6W 80 KT 36HR VT 10/1200Z 16.6N 126.1W 70 KT 48HR VT 11/0000Z 17.1N 127.7W 60 KT 72HR VT 12/0000Z 17.5N 130.5W 45 KT 96HR VT 13/0000Z 17.5N 132.5W 35 KT 120HR VT 14/0000Z 16.5N 134.5W 25 KT $$ FORECASTER BEVEN