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Hurricane HERNAN


ZCZC MIATCDEP4 ALL
TTAA00 KNHC DDHHMM
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
 
NNNN


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Page last modified: Tuesday, 21-Apr-2009 12:09:38 UTC