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HURRICANE HERNAN DISCUSSION NUMBER 17
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT TUE SEP 03 2002
HERNAN CONTINUES ON A WEAKENING TREND AS EVIDENCED BY WARMING OF
THE CONVECTION SURROUNDING THE EYE. LATEST DVORAK INTENSITY
ESTIMATES ARE 5.0 FROM TAFB AND SAB. THEREFORE...THE INITIAL
INTENSITY WILL BE DECREASED TO 90 KT FOR THIS FORECAST PACKAGE.
LATEST SATELLITE IMAGERY INDICATES THAT THE INNER EYE WALL IS
BECOMING LESS DEFINED WITH TIME. THIS MAY BE DUE TO THE DEVELOPMENT
OF AN OUTER EYE WALL FORMING AS SUGGESTED BY A TRMM OVERPASS FROM
0649 UTC. THIS WOULD COMPLETE THE EYEWALL REPLACEMENT CYCLE THAT
BEGAN A LITTLE OVER 24 HOURS AGO. ARRESTED WEAKENING OR
RESTRENGTHENING TYPICALLY OCCURS WITH EYEWALL REPLACEMENT
CYCLES...ALTHOUGH IN THIS CASE HERNAN MAY NOT HAVE ENOUGH TIME TO
STRENGTHEN SIGNIFICANTLY DUE TO ITS EXPECTED PASSING OVER SUB-26C
SEA SURFACE TEMPERATURES IN ABOUT 12-24 HOURS. TO ACCOUNT FOR THE
POSSIBILITY OF RESTRENGTHENING...THE WEAKENING TREND WILL BE SLOWED
DOWN FOR THE FIRST 12 HOURS...WITH MORE RAPID WEAKENING THEREAFTER
AS INDICATED BY THE SHIPS MODEL AND ALSO BY THE PREVIOUS FORECAST.
THE INITIAL MOTION IS 280/9 WHICH IS SLIGHTLY TO THE SOUTH OF THE
PREVIOUS TRACK...HOWEVER THE TRACK FORECAST PHILOSOPHY REMAINS
MOSTLY UNCHANGED. HERNAN WILL MAINTAIN A WEST TO WEST-NORTHWEST
TRACK FOR ABOUT 12-24 HOURS BEFORE MAKING A GRADUAL TURN TO THE
NORTHWEST AND THEN NORTH BY THE END OF THE FORECAST PERIOD AS THE
CYCLONE BECOMES INFLUENCED BY A DEVELOPING MID/UPPER LEVEL TROUGH
OFF THE CALIFORNIA COAST. THIS TRACK IS AN UPDATE OF THE PREVIOUS
FORECAST AND IN CLOSE AGREEMENT WITH MUCH OF THE NHC GUIDANCE.
FORECASTER JARVINEN/AGUIRRE
FORECAST POSITIONS AND MAX WINDS
INITIAL 03/0900Z 18.9N 118.7W 90 KTS
12HR VT 03/1800Z 19.3N 120.0W 80 KTS
24HR VT 04/0600Z 20.6N 121.4W 70 KTS
36HR VT 04/1800Z 22.0N 122.3W 55 KTS
48HR VT 05/0600Z 23.4N 123.4W 40 KTS
72HR VT 06/0600Z 26.3N 123.6W 25 KTS
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