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TROPICAL STORM HERNAN DISCUSSION NUMBER 25
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT THU SEP 05 2002
HERNAN CONTINUES TO WEAKEN WITH AN OVERALL DECREASE IN CLOUD TOP
TEMPERATURES. HOWEVER...SOME NEW BANDS OF MODERATE CONVECTION HAVE
FORMED TO THE SOUTH AND WEST OF THE CENTER. CURRENT DVORAK INTENSITY
ESTIMATES ARE 30 KTS FROM TAFB AND 35 KNOTS FROM SAB AND AFWA. THE
INITIAL INTENSITY IS LOWERED FROM THE PREVIOUS ADVISORY TO 35 KNOTS.
DESPITE THE WEAKENING TREND...UPPER LEVEL OUTFLOW REMAINS GOOD.
THE INITIAL MOTION ESTIMATE IS 310/5. HERNAN HAS CONTINUED TO SLOW
ITS FORWARD SPEED AS IT BECOMES AN INCREASINGLY SHALLOW SYSTEM.
THE DOMINANT STEERING FLOW IS NOW THE LOW LEVEL EASTERLIES ON THE
SOUTHERN EXTENT OF THE SUBTROPICAL RIDGE. THE OFFICIAL FORECAST
TRACK IS SOUTH OF THE PREVIOUS TRACK AND IS IN BEST AGREEMENT WITH
THE UKMET GLOBAL MODEL AND IS SIMILAR TO THE AVN..NOGAPS...AND GFDL
WHICH INDICATE A DRIFT TO THE SOUTHWEST.
HERNAN IS FORECAST TO CONTINUE WEAKENING AS IT REMAINS OVER
RELATIVELY COOL WATER. HOWEVER...THE FAVORABLE UPPER LEVEL OUTFLOW
PATTERN AND THE WESTWARD TRACK SHOULD KEEP THE SYSTEM IN A LESS
HOSTILE ENVIRONMENT THAN PREVIOUSLY EXPECTED. THE INTENSITY FORECAST
IS A LITTLE HIGHER THAN THE SHIPS INTENSITY MODEL...WHICH DISSIPATES
HERNAN BY 24 HOURS. HOWEVER...IF HERNAN TAKES A MORE SOUTHWARD
TRACK AS INDICATED BY THE AVN...NOGAPS...AND GFDL MODELS...THEN
WEAKENING WILL NOT BE AS FAST AS CURRENTLY FORECAST.
FORECASTER STEWART/RHOME
FORECAST POSITIONS AND MAX WINDS
INITIAL 05/0900Z 22.1N 123.9W 35 KTS
12HR VT 05/1800Z 22.5N 124.4W 30 KTS
24HR VT 06/0600Z 22.8N 125.1W 25 KTS
36HR VT 06/1800Z 23.0N 126.0W 25 KTS...DISSIPATING
48HR VT 07/0600Z 23.0N 126.8W 20 KTS...REMNANT LOW
72HR VT 08/0600Z 22.5N 128.5W 20 KTS...REMNANT LOW
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