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Hurricane HERNAN


ZCZC MIATCDEP4 ALL
TTAA00 KNHC DDHHMM
HURRICANE HERNAN DISCUSSION NUMBER  12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP092008
800 AM PDT SAT AUG 09 2008
 
THE EYE OF HERNAN HAS BECOME DRAMATICALLY MORE DISTINCT IN GOES
INFRARED IMAGERY DURING THE PAST SEVERAL HOURS...AND IT IS NOW
SURROUNDED BY A SOLID RING OF CLOUD TOPS COLDER THAN -70C.  AMSR-E
MICROWAVE IMAGERY AT 0937 UTC DEPICTED A SINGLE COMPLETE EYEWALL
AND AN EYE DIAMETER OF 20-25 N MI.  THERE SEEMS LITTLE DOUBT THAT
HERNAN HAS BECOME A MAJOR HURRICANE... HAVING UNDERGONE RAPID
INTENSIFICATION SINCE YESTERDAY.  THIS PROVIDES YET ANOTHER EXAMPLE
OF THE INABILITY OF MODEL GUIDANCE...AND THEREFORE THE HUMAN
FORECASTER...TO CAPTURE AND CONVEY THE TIMING AND MAGNITUDE OF THESE
EPISODES WITH A DETERMINISTIC INTENSITY FORECAST.  THE EXACT
INITIAL INTENSITY IS A LITTLE UNCERTAIN.  SUBJECTIVE DVORAK
ESTIMATES AT 12Z FROM TAFB AND SAB WERE BOTH 102 KT...WHILE
OBJECTIVE ESTIMATES ARE ABOUT 115 KT.  THE ADVISORY INTENSITY
COMPROMISES AT 105 KT...BUT WITHOUT ACTUAL WIND DATA TO KNOW ANY
BETTER...IT IS POSSIBLE HERNAN IS A LITTLE STRONGER THAN THIS
ESTIMATE.  UNDERLYING SEA-SURFACE TEMPERATURES ARE ABOUT 27 CELSIUS
NOW...AND ALONG THE FORECAST TRACK THE HURRICANE WILL CROSS THE 26
CELSIUS ISOTHERM IN ROUGHLY 24 HOURS...SO A GRADUAL WEAKENING TREND
IS FORECAST TO BEGIN AROUND THAT TIME.  A FASTER DECLINE IS
FORECAST IN A COUPLE OF DAYS ONCE THE CYCLONE REACHES SUBSTANTIALLY
COOLER WATERS.  THE OFFICIAL FORECAST IS ABOVE THE OBJECTIVE
GUIDANCE FOR THE NEXT DAY OR TWO...THEN SHOWS A FASTER WEAKENING
THAN THE MODELS DUE TO THE SMALL SIZE OF THE CYCLONE.

HERNAN HAS TURNED A LITTLE MORE TO THE RIGHT...AND ONE MUST GIVE
SOME OF THE MODELS CREDIT FOR CORRECTLY FORECASTING THIS BEND
YESTERDAY.  THE INITIAL MOTION ESTIMATE IS 295/8...BUT A GRADUAL
TURN BACK TO THE LEFT IS FORECAST BY ALL OF THE DYNAMICAL MODELS AS
THE SUBTROPICAL RIDGE BUILDS WESTWARD OVER THE EASTERN PACIFIC
DURING THE NEXT COUPLE OF DAYS.  BEYOND THAT TIME...A WEAKENING
HERNAN IS EXPECTED TO BECOME A MORE SHALLOW SYSTEM AND TURN
WESTWARD AND EVENTUALLY WEST-SOUTHWESTWARD IN THE LOW- TO MID-LEVEL
FLOW.  THE NEW OFFICIAL TRACK FORECAST IS ALMOST IDENTICAL TO THE
PREVIOUS ONE AND IS CLOSE TO THE MODEL CONSENSUS.
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/1500Z 15.7N 123.3W   105 KT
 12HR VT     10/0000Z 16.2N 124.4W   105 KT
 24HR VT     10/1200Z 16.8N 125.9W    95 KT
 36HR VT     11/0000Z 17.3N 127.3W    80 KT
 48HR VT     11/1200Z 17.6N 128.7W    65 KT
 72HR VT     12/1200Z 18.0N 131.0W    45 KT
 96HR VT     13/1200Z 17.5N 133.5W    35 KT
120HR VT     14/1200Z 16.5N 136.0W    30 KT
 
$$
FORECASTER KNABB
 
NNNN


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