Tropical Storm HERNAN

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TROPICAL STORM HERNAN DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP092008
200 PM PDT MON AUG 11 2008
 
HERNAN WAS DIAGNOSED AS A MARGINAL HURRICANE AT THE 18Z SYNOPTIC
TIME...BUT SINCE THEN THE LOW-LEVEL AND UPPER-LEVEL CIRCULATIONS
HAVE STARTED TO DECOUPLE. BASED ON THIS MOST RECENT SATELLITE
TREND...HERNAN HAS BEEN DOWNGRADED TO A 60-KT TROPICAL STORM AT THE
21Z ADVISORY TIME.

NOW THAT THE LOW- TO MID-LEVEL CIRCULATIONS HAVE STARTED TO DECOUPLE
FROM THE UPPER-LEVEL CIRCULATION...HERNAN IS EXPECTED TO MAKE MORE
OF A WESTWARD AND WEST-SOUTHWESTWARD MOTION AS IT COMES UNDER THE
INFLUENCE OF THE STRONG LOW-LEVEL RIDGING TO THE NORTH OF THE
CYCLONE. THIS FORECAST SCENARIO IS CONSISTENT WITH THE CONSENSUS OF
ALL OF THE NHC MODELS. HERNAN OR ITS REMNANT CIRCULATION IS
EXPECTED TO CROSS INTO THE CENTRAL PACIFIC BASIN ON THURSDAY.

HERNAN WILL BE PASSING OVER SUB-24C SEA SURFACE TEMPERATURES FOR THE
NEXT 48 HOURS...WHICH SHOULD INDUCE CONTINUED WEAKENING. HOWEVER...
BY 72 HOURS...THE CYCLONE WILL BE MOVING OVER 25C AND WARMER SSTS
AND ALSO BE UNDER THE INFLUENCE OF LIGHT SOUTHEASTERLY UPPER-LEVEL
SHEAR...WHICH COULD ALLOW FOR SOME REDEVELOPMENT OF CONVECTION THAT
WOULD HELP MAINTAIN THE SYSTEM AS A TROPICAL CYCLONE RATHER THAN A
REMNANT LOW AT DAYS 4 AND 5.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      11/2100Z 19.0N 131.2W    60 KT
 12HR VT     12/0600Z 18.9N 132.3W    55 KT
 24HR VT     12/1800Z 18.5N 133.9W    45 KT
 36HR VT     13/0600Z 18.0N 135.4W    40 KT
 48HR VT     13/1800Z 17.6N 137.2W    35 KT
 72HR VT     14/1800Z 16.5N 140.5W    30 KT
 96HR VT     15/1800Z 16.0N 144.5W    25 KT...REMNANT LOW
120HR VT     16/1800Z 16.0N 148.5W    25 KT...REMNANT LOW
 
$$
FORECASTER STEWART/PASCH
 
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