Tropical Storm HERNAN

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TROPICAL STORM HERNAN DISCUSSION NUMBER  24
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP092008
800 AM PDT TUE AUG 12 2008
 
HERNAN HAS VERY LITTLE DEEP CONVECTION NOW THAT IT IS OVER SEA
SURFACE TEMPERATURES NEAR 23C. AN AVERAGE OF THE TAFB AND SAB
SATELLITE CLASSIFICATIONS PROVIDES AN ESTIMATE OF 45 KT AND THE
MOST RECENT ADT IS NOW DOWN TO 30 KT. GIVEN THE DEGRADATION OF THE
CLOUD PATTERN...THE INITIAL INTENSITY IS SET AS 40 KT AS A
COMPROMISE OF THE SUBJECTIVE AND OBJECTIVE TECHNIQUES. SINCE IT IS
UNLIKELY THAT HERNAN WILL BE ABLE TO GENERATE PERSISTENT CONVECTION
OVER THE COOLER WATERS...THE CYCLONE IS EXPECTED TO WEAKEN TO A
TROPICAL DEPRESSION LATER TODAY. THE NEW FORECAST SHOWS HERNAN
DISSIPATING INTO AN OPEN WAVE WITHIN THE TRADE WIND BELT SOUTHEAST
OF HAWAII BY DAY 5...IF NOT SOONER...IN LINE WITH THE GLOBAL MODEL
GUIDANCE.
 
THE INITIAL MOTION IS JUST SOUTH OF DUE WEST AT 260/8. THE
SHORT-TERM MOTION WILL BE DICTATED BY A MID-LEVEL RIDGE AXIS
EXTENDING SOUTHWEST OF SOUTHERN CALIFORNIA DIRECTLY TOWARDS
HERNAN...WHICH WILL FORCE A MORE WEST-SOUTHWESTWARD MOTION. ONCE
HERNAN WEAKENS TO A REMNANT LOW...IT IS EXPECTED TO TURN WEST WITH
AN INCREASE IN SPEED AS IT IS STEERED BY THE LOW-LEVEL SUBTROPICAL
RIDGE.
 

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      12/1500Z 18.3N 133.6W    40 KT
 12HR VT     13/0000Z 18.1N 134.7W    30 KT
 24HR VT     13/1200Z 17.7N 136.2W    30 KT
 36HR VT     14/0000Z 17.2N 137.7W    25 KT...REMNANT LOW
 48HR VT     14/1200Z 16.7N 139.2W    25 KT...REMNANT LOW
 72HR VT     15/1200Z 15.5N 143.5W    20 KT...REMNANT LOW
 96HR VT     16/1200Z 15.0N 148.0W    20 KT...REMNANT LOW
120HR VT     17/1200Z...DISSIPATED
 
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FORECASTER BERG/BROWN
 
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