Hurricane HERNAN

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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
 
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