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HURRICANE HERNAN DISCUSSION NUMBER  20
NATIONAL WEATHER SERVICE MIAMI FL
8 PM PDT TUE SEP 03 2002
 
SATELLITE IMAGES THIS EVENING INDICATE THAT HERNAN CONTINUES TO 
GRADUALLY WEAKEN.  THE ONCE CLEARLY VISIBLE EYE HAS BECOME 
CLOUD-FILLED AND CONVECTIVE TOPS HAVE WARMED.  DVORAK INTENSITY 
ESTIMATES FROM THE THREE SATELLITE AGENCIES ARE 4.0-4.5...WITH AN 
OBJECTIVE T-NUMBER OF 4.5.  THE INITIAL INTENSITY WILL BE 70 KT FOR 
THIS FORECAST PACKAGE.  CONTINUED WEAKENING IS EXPECTED AS HERNAN 
MOVES OVER PROGRESSIVELY COOLER WATER...AS WELL AS INTO INCREASING 
WESTERLY SHEAR AHEAD OF AN APPROACHING MID/UPPER LEVEL TROUGH LATE 
IN THE FORECAST PERIOD.  HERNAN IS FORECAST TO DISSIPATE BY 72 
HOURS.    

HERNAN IS MOVING 290 DEGREES AT ABOUT 8 KNOTS...SLIGHTLY SLOWER AND
TO THE LEFT OF THE PREVIOUS FORECAST.  THIS WEST-NORTHWEST MOTION IS
EXPECTED TO CONTINUE FOR ABOUT 12 HOURS AS THE CYCLONE NEARS THE
WESTERN EDGE OF THE SUBTROPICAL RIDGE...WITH A GRADUAL TURN TO THE
NORTHWEST THEN NORTH BY THE END OF THE FORECAST PERIOD AS THE
ADVANCING MID/UPPER LEVEL TROUGH BREAKS DOWN THE RIDGE.  NHC TRACK
GUIDANCE IS A BIT DIVERGENT...ESPECIALLY IN THE LATTER PART OF THE
FORECAST.  THE NCEP GLOBAL MODEL...UKMET MODEL...AND SHALLOW AND
MEDIUM-LAYER BAM MODELS CONTINUE TO MOVE HERNAN WEST-NORTHWESTWARD
BEYOND 36 HOURS...WHILE THE NAVY NOGAPS MODEL TURNS THE SYSTEM TO
THE NORTH AND NORTHEAST AHEAD OF THE MID/UPPER TROUGH.  DUE TO THE
EXPECTED WEAK AND SHALLOW NATURE OF THE CYCLONE BEYOND 36 HOURS...
THE WEST-NORTHWESTWARD SOLUTIONS ARE NOT TOTALLY UNREASONABLE AS THE
STEERING INFLUENCE FROM THE MID/UPPER TROUGH WOULD BE LESSENED.  THE
FORECAST TRACK IS VERY SIMILAR TO THE PREVIOUS FORECAST THROUGH 48
HOURS...THEN A BIT SLOWER AND TO THE LEFT BY 72 HOURS.  HOWEVER...
THERE IS A POSSIBILITY THAT A WEAK NON-CONVECTIVE REMNANT LOW MAY 
APPROACH THE EXTREME SOUTHERN CALIFORNIA COAST OR NORTHERN BAJA IN 
ABOUT 5 DAYS...WITH THE MID AND HIGH LEVEL MOISTURE POSSIBLY 
SPREADING OVER THIS AREA WELL AHEAD OF THE LOW.

FORECASTER STEWART/MOLLEDA

FORECAST POSITIONS AND MAX WINDS
 
INITIAL     04/0300Z 19.7N 121.2W    70 KTS
12HR VT     04/1200Z 20.2N 122.4W    65 KTS
24HR VT     05/0000Z 21.5N 123.7W    55 KTS
36HR VT     05/1200Z 23.0N 124.6W    45 KTS
48HR VT     06/0000Z 24.5N 124.5W    30 KTS
72HR VT     07/0000Z 26.5N 124.0W    25 KTS...DISSIPATING
 
 
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