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TROPICAL STORM DOLLY DISCUSSION NUMBER 23
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT TUE SEP 03 2002
THE INITIAL INTENSITY REMAINS A VERY GENEROUS 45 KT BASED ON
SATELLITE INTENSITY ESTIMATES OF 45 KT FROM TAFB AND AFWA...AND
55 KT FROM SAB. HOWEVER...SATELLITE IMAGERY DURING PAST 3 HOURS
INDICATES THE CONVECTION HAS WEAKENED AND THE LOW-LEVEL CENTER HAS
BECOME EXPOSED AGAIN TO THE SOUTHWEST OF THE STRONGEST CONVECTION.
BUT RATHER THAN YOYO-ING THE INTENSITY UP AND DOWN...I HAVE OPTED
INSTEAD TO MAINTAIN THE PREVIOUS INTENSITY SINCE DOLLY IS PREPARING
TO GO THROUGH THE DIURNAL CONVECTIVE MAXIMUM PERIOD AND THERE COULD
BE ANOTHER FLARE UP OF THUNDERSTORMS NEAR THE CENTER. HOWEVER...IF
CONVECTION DOES NOT RE-DEVELOP...THEN THE INTENSITY WILL CERTAINLY
BE LOWERED ON THE NEXT ADVISORY.
THE INITIAL MOTION ESTIMATE IS 360/10. THERE HAS BEEN A MAJOR
WESTWARD SHIFT IN THE NHC MODEL GUIDANCE...ESPECIALLY AMONG THE
AVN...GFDL...NOGAPS AND GFDN MODELS. ONLY THE UKMET HAS REMAINED
CONSISTENT OVER THE LAST COUPLE OF MODEL RUNS. THERE IS ALSO
CONSIDERABLE DIVERGENCE IN THE NHC MODEL SUITE AFTER 48 HOURS...WITH
THE AVN BEING THE FASTEST AND FARTHEST LEFT OF ALL THE MODELS. IT
TAKES DOLLY TO SOUTHEAST NEWFOUNDLAND IN 72 HOURS AND IS JUST A
LITTLE WEST OF THE GFDN AND GFDL POSITIONS FOR THE SAME TIME. THE
OFFICIAL TRACK WAS SHIFTED WEST OF AND FASTER THAN THE PREVIOUS
FORECAST...BUT NOT NEARLY AS FAR WEST OR AS FAST AS THE AVN MODEL.
THE AVN 10-MEMBER ENSEMBLE MEAN FORECAST IS MUCH SLOWER AND FARTHER
EAST THAN THE AVN...AND THIS SCENARIO WAS FOLLOWED SINCE IT IS
SIMILAR TO THE NOGAPS AND UKMET SOLUTIONS.
THERE WILL LIKELY BE DIURNAL FLUCTUATIONS IN THE INTENSITY FOR THE
NEXT 36 TO 48 HOURS. HOWEVER...NO SIGNIFICANT STRENGTHENING IS
FORECAST SINCE DOLLY IS EXPECTED TO REMAIN UNDER 20 TO 25 KT
SOUTHWESTERLY TO SOUTHERLY SHEAR. AFTER 48 HOURS AND ESPECIALLY BY
72 HOURS...DOLLY IS FORECAST TO MOVE UNDER AN AMPLIFYING RIDGE TO
THE EAST OF A DIGGING AND NEGATIVELY-TILTED UPPER-LEVEL TROUGH. THIS
SHOULD ALLOW THE SHEAR TO WEAKEN SOME AND MAY PERMIT DOLLY TO
STRENGTHEN A LITTLE SINCE THE CYCLONE WILL STILL BE OVER 26C SSTS.
HOWEVER...THE OFFICIAL INTENSITY FORECAST IS NOT NEARLY AS ROBUST AS
THE SHIPS AND GFDL MODELS WHICH BRING DOLLY TO 76 KT AND 104 KT...
RESPECTIVELY...BY 72 HOURS.
FORECASTER STEWART
FORECAST POSITIONS AND MAX WINDS
INITIAL 04/0300Z 23.6N 52.4W 45 KTS
12HR VT 04/1200Z 25.1N 52.3W 40 KTS
24HR VT 05/0000Z 27.6N 52.1W 40 KTS
36HR VT 05/1200Z 30.1N 51.8W 40 KTS
48HR VT 06/0000Z 33.0N 51.0W 45 KTS
72HR VT 07/0000Z 39.0N 48.5W 50 KTS
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