Tropical Storm HERNAN

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TROPICAL STORM HERNAN DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP092008
200 PM PDT THU AUG 07 2008
 
THE OVERALL SATELLITE PRESENTATION OF HERNAN HAS INDICATED A GRADUAL
INCREASE IN ORGANIZATION TODAY...BUT MICROWAVE IMAGERY SUGGESTS
THAT THE LOW-LEVEL CIRCULATION CENTER IS STILL A LITTLE NORTH OF
THE MID-LEVEL CENTER...WHICH IN GEOSTATIONARY VISIBLE IMAGERY LOOKS
LIKE AN EYE THAT IS TRYING TO FORM. SUBJECTIVE DVORAK INTENSITY
ESTIMATES AT 18Z WERE A CONSENSUS 55 KT...AND QUIKSCAT EARLIER
TODAY AROUND 1340Z RETRIEVED WINDS OF 50-55 KT. IT IS POSSIBLE THAT
HERNAN HAS BECOME A LITTLE STRONGER THAN THE LATEST DVORAK
ESTIMATES SUGGEST...BUT GIVEN THE SLIGHTLY TILTED STRUCTURE EVIDENT
IN MICROWAVE IMAGERY...THE ADVISORY INTENSITY WILL BE SET TO 55 KT.
NEVERTHELESS...HERNAN APPEARS TO BE ON THE CUSP OF BECOMING A
HURRICANE...AND ALL OF THE OBJECTIVE INTENSITY MODELS FORECAST THAT
TO HAPPEN WITHIN 24 HOURS. THE OFFICIAL FORECAST CALLS FOR HERNAN
TO REACH HURRICANE STATUS A LITTLE SOONER THAN...AND TO PEAK A
LITTLE HIGHER THAN...MOST OF THE GUIDANCE. THE CYCLONE HAS ABOUT
TWO DAYS UNTIL IT REACHES SSTS OF 26 CELSIUS...SO STEADY WEAKENING
IS FORECAST BEYOND THAT TIME...AND AT A LITTLE FASTER RATE THAN
SHOWN BY THE SHIPS AND LGEM.

THE INITIAL MOTION ESTIMATE IS 285/12...BUT IS A LITTLE UNCERTAIN
SINCE IT IS NOT CRYSTAL CLEAR IN MICROWAVE IMAGERY WHERE THE
LOW-LEVEL CENTER IS LOCATED.  DESPITE NOT KNOWING THOSE
DETAILS...AND EVEN THOUGH THERE IS A LITTLE SPREAD IN THE TRACK
MODELS...THE OVERALL SYNOPTIC PATTERN IS RELATIVELY STRAIGHTFORWARD
WITH A SUBTROPICAL RIDGE OF MODERATE STRENGTH FORECAST TO REMAIN IN
PLACE OVER THE EASTERN PACIFIC FOR THE NEXT SEVERAL DAYS.  HERNAN
SHOULD CONTINUE WEST-NORTHWESTWARD UNTIL REACHING THE COOLER WATERS
IN A FEW DAYS...FOLLOWED BY A WEAKER CYCLONE EVENTUALLY TURNING
WESTWARD IN THE LOW-LEVEL FLOW.  THE NEW OFFICIAL TRACK IS A LITTLE
SOUTH OF THE PREVIOUS ONE THROUGH ABOUT 48 HOURS...BUT IS OTHERWISE
NOT CHANGED THAT MUCH...AND IT IS SIMILAR TO THE MODEL CONSENSUS.
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      07/2100Z 14.8N 116.7W    55 KT
 12HR VT     08/0600Z 15.3N 118.1W    65 KT
 24HR VT     08/1800Z 15.8N 119.8W    70 KT
 36HR VT     09/0600Z 16.5N 121.6W    70 KT
 48HR VT     09/1800Z 17.1N 123.4W    70 KT
 72HR VT     10/1800Z 18.0N 126.5W    50 KT
 96HR VT     11/1800Z 19.0N 130.0W    35 KT
120HR VT     12/1800Z 19.0N 133.5W    25 KT...REMNANT LOW
 
$$
FORECASTER KNABB
 
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