JUAN #12 - DISCUSSION

[AussieMark]

000
WTNT45 KNHC 280855
TCDAT5
HURRICANE JUAN DISCUSSION NUMBER 12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT SUN SEP 28 2003

CLOUD TOPS AROUND THE EYE HAVE COOLED...WITH SOME TOPS COLDER THAN
-75C...AND DVORAK CLASSIFICATIONS REMAIN T5.0...OR 90 KT...FROM
BOTH TAFB AND SAB. THE EYE HAS ALSO DECREASED IN SIZE AND THE 3-HR
AVERAGE DVORAK OBJECTIVE T-NUMBER IS T4.9...OR 88 KT. THEREFORE...
THE INITIAL INTENSITY REMAINS AT 90 KT FOR THIS ADVISORY.

THE INITIAL MOTION ESTIMATE IS 355/10...EVEN THOUGH THE PAST 6-HR
MOTION HAS BEEN 340/09. THE LAST FEW SATELLITE POSITIONS...ALONG
WITH WATER VAPOR MOTIONS...SUGGEST THAT JUAN MAY BE FINALLY MAKING
THE TURN MORE TOWARD THE NORTH THAT THE GLOBAL MODELS HAVE BEEN
FORECASTING THE PAST 24 HOURS. THERE IS A SLIGHT CONFLICT BETWEEN
THE VARIOUS MODELS WITH THE GFS AND CANADIAN MODELS BRINGING A
SURFACE LOW CENTER WEST OF NOVA SCOTIA AND INTO EXTREME EASTERN
MAINE...WHILE THE UKMET...GFDL...AND NOGAPS MODELS TAKE JUAN OVER
OR JUST WEST OF HALIFAX NOVA SCOTIA. HOWEVER...THE CANADIAN AND GFS
850-500 MB VORTICITY CENTERS ARE FORECAST TO REMAIN VERTICALLY
STACKED AND PASS JUST WEST OF HALIFAX IN ABOUT 18-21 HOURS...SO THE
OFFICIAL FORECAST TRACK WAS ONLY NUDGED SLIGHTLY TO THE EAST OF THE
PREVIOUS FORECAST TRACK. THIS IS CONSISTENT WITH ALL OF THE MODELS
FORECASTING THE 500-200 MB MEAN WIND FLOW TO BE FROM A SOUTH TO
SOUTH-SOUTHWESTERLY DIRECTION AFTER 12 HOURS...WHICH SHOULD KEEP
JUAN MOVING IN A GENERAL NORTHERLY DIRECTION. NOTE...AN 18-HR/00Z
FORECAST POSITION WOULD PLACE JUAN NEAR 43.3N 64.2W AND 70-KT.

SINCE JUAN IS FORECAST TO BEGIN ACCELERATING LATER THIS MORNING AND
UNTIL LANDFALL...THERE WILL LIKELY NOT BE ANY SIGNIFICANT INCREASE
IN THE VERTICAL SHEAR. THEREFORE...THE WEAKENING TREND THAT IS
FORECAST IS MAINLY DUE TO THE CYCLONE PASSING OVER MUCH COOLER SSTS
NORTH OF 40N LATITUDE. ALSO...THE COOLER WATER MAY CAUSE THE
BOUNDARY LAYER TO BECOME MORE STABLE...WHICH MAY NOT ALLOW ALL OF
THE STRONGER WINDS ALOFT TO COME DOWN TO THE SURFACE. HOWEVER...
JUAN IS STILL EXPECTED TO BE NEAR HURRICANE STRENGTH AT LANDFALL.

SINCE JUAN IS EXPECTED TO MAKE LANDFALL IN THE VICINITY OF HALIFAX
BETWEEN 00-03Z THIS EVENING AT ASTRONOMICAL HIGH TIDE...SOME STORM
SURGE FLOODING MAY OCCUR ALONG THE SOUTH COAST OF NOVA SCOTIA
...ESPECIALLY IN HARBORS AND INLETS IN AND AROUND HALIFAX.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 28/0900Z 37.6N 64.1W 90 KT
12HR VT 28/1800Z 40.7N 64.3W 80 KT
24HR VT 29/0600Z 46.0N 63.9W 60 KT...INLAND BECOMING E.T.
36HR VT 29/1800Z 53.8N 62.9W 40 KT...EXTRATROPICAL
48HR VT 30/0600Z...ABSORBED BY LARGER EXTRATROPICAL LOW