Hurricane HERNAN

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HURRICANE HERNAN DISCUSSION NUMBER  15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP092008
200 AM PDT SUN AUG 10 2008
 
HERNAN CONTINUES TO WEAKEN AS IT MOVES OVER COOLER SSTS AND THE
INITIAL INTENSITY IS LOWERED TO 85 KT BASED ON A BLEND OF THE
SUBJECTIVE DVORAK FINAL T AND CI NUMBERS.  ADDITIONAL WEAKENING IS
ANTICIPATED AND HERNAN COULD DROP BELOW HURRICANE STRENGTH WITHIN
THE NEXT 24 HOURS.  SSTS LEVEL OFF IN ABOUT 2 DAYS THEN BEGIN TO
RISE SO A SLOWER RATE OF DECAY IS SHOWN AT THE EXTENDED FORECAST
TIMES...AND HERNAN COULD CLING TO ITS STATUS AS A TROPICAL CYCLONE
FOR SEVERAL DAYS.
 
THE INITIAL MOTION ESTIMATE IS ESSENTIALLY UNCHANGED 305/09. AN
UPPER-LEVEL TROUGH TO THE NORTHWEST OF HERNAN IS FORECAST TO BE
REPLACED BY A WEAK RIDGE DURING THE NEXT DAY OR SO RESULTING IN A
GRADUAL TURN TOWARDS THE WEST. BEYOND 48 HOURS...A TURN MORE
SOUTHWESTWARD IS FORECAST AS THE WEAKENING CYCLONE IS STEERED BY
THE NORTHEASTERLY LOW/MID-LEVEL FLOW. THERE REMAINS SPREAD IN THE
TRACK GUIDANCE...WITH THE BAM MODELS AND THE HWRF CALLING FOR A
SLOWER WESTWARD TURN RESULTING IN THOSE MODELS LYING ALONG THE
NORTHERN EDGE OF THE GUIDANCE ENVELOPE. CONVERSELY...THE GFS AND
UKMET MODELS SHOW A MUCH SHARPER WESTWARD AND SOUTHWESTWARD TURN
WITH THOSE MODELS LYING ALONG THE SOUTHERN EDGE OF THE GUIDANCE
ENVELOPE. THE OFFICIAL TRACK FORECAST IS A LITTLE NORTH OF THE
MODEL CONSENSUS AND CLOSE TO THE GFDL MODEL THROUGH ABOUT 48
HOURS...THEN ALONG BUT A LITTLE SLOWER THAN THE MODEL CONSENSUS
THEREAFTER.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      10/0900Z 17.3N 125.7W    85 KT
 12HR VT     10/1800Z 17.7N 126.7W    70 KT
 24HR VT     11/0600Z 18.0N 128.1W    60 KT
 36HR VT     11/1800Z 18.1N 129.4W    50 KT
 48HR VT     12/0600Z 18.0N 130.5W    45 KT
 72HR VT     13/0600Z 17.0N 133.0W    40 KT
 96HR VT     14/0600Z 16.5N 135.0W    35 KT
120HR VT     15/0600Z 16.0N 138.0W    30 KT
 
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FORECASTER RHOME
 
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