ISABEL #17 - DISCUSSION

[AussieMark]

000
WTNT43 KNHC 100842
TCDAT3
HURRICANE ISABEL DISCUSSION NUMBER 17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT WED SEP 10 2003

SATELLITE IMAGES SHOW A DISTINCT EYE SURROUNDED BY DEEP CONVECTION.
THE OUTFLOW TO THE WEST AND SOUTH IS IMPRESSIVE BUT IS SOMEWHAT
LIMITED TO THE EAST. SUBJECTIVE T-NUMBERS ARE 6.0 AND 5.5 FROM TAFB
AND SAB..RESPECTIVELY. THE LATEST OBJECTIVE T-NUMBERS ARE BACK UP
TO 6.0 ON THE DVORAK SCALE. INITIAL INTENSITY REMAINS AT 115 KNOTS.
THERE IS NO SHEAR AND THE OCEAN IS INCREASINGLY WARMER. THESE
ENVIRONMENTAL CONDITIONS SHOULD ALLOW SOME ADDITIONAL
STRENGTHENING. BUT...IN MAJOR HURRICANES...CHANGES IN INTENSITY ARE
CONTROLLED IN GENERAL BY EYEWALL THERMODYNAMICS. THEREFORE...SOME
FLUCTUATIONS IN INTENSITY ARE INDICATED TO REFLECT UNCERTAINTIES.

THE FORECAST TRACK IS BECOMING RATHER INTERESTING. LAST FEW
SATELLITE IMAGES SUGGEST THAT ISABEL HAS BEGUN TO TURN TOWARD THE
WEST. THE INITIAL MOTION IS NOW ESTIMATED AT 275 DEGREES AT 12
KNOTS. HOWEVER...A LONGER TERM AVERAGE IS STILL TOWARD THE
WEST-NORTHWEST. GLOBAL MODELS CONTINUE TO SHOW THE DEVELOPMENT OF A
STRONG SUBTROPICAL RIDGE NORTH OF ISABEL. DEPENDING UPON THE
FORECAST STRENGTH OF THE RIDGE...EACH MODEL MOVES ISABEL EITHER
WEST OR WEST-NORTHWEST. THE GFS HAS THE STRONGEST RIDGE AND IS
PRODUCING THE SOUTHERMOST AND DANGEROUS TRACK. THE UK HAS A WEAKER
RIDGE WITH THE NORTHERMOST TRACK BUT STILL INDICATING A
WEST-NORTHWEST TO WEST MOTION. THE OFFICIAL FORECAST IS IN BETWEEN
THESE TWO SOLUTIONS. THE NOGAPS APPEARS TO BE VERY SLOW BUT IT IS
SHOWING THE SAME WEST TO WEST-NORTHWEST TREND. THE BOTTOM LINE IS
THAT A RIDGE IS FORECAST TO DEVELOP BETWEEN THE U.S. EAST COAST AND
BERMUDA. THIS PATTERN WOULD MAINTAIN ISABEL ON A GENERAL WEST TO
WEST-NORTHWEST TRACK FOR THE NEXT SEVERAL DAYS...KEEPING THE CORE
OF THE HURRICANE AWAY FROM THE NORTHERN LEEWARD ISLANDS.

IF THE CURRENT WESTWARD TREND CONTINUES...THE OFFICIAL FORECAST WILL
HAVE TO BE ADJUSTED SLIGHTLY SOUTHWARD IN THE NEXT TERM.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 10/0900Z 20.9N 50.2W 115 KT
12HR VT 10/1800Z 21.5N 52.1W 115 KT
24HR VT 11/0600Z 21.5N 54.2W 115 KT
36HR VT 11/1800Z 21.5N 56.0W 115 KT
48HR VT 12/0600Z 21.5N 58.0W 115 KT
72HR VT 13/0600Z 21.5N 60.5W 115 KT
96HR VT 14/0600Z 22.0N 63.5W 110 KT
120HR VT 15/0600Z 23.0N 67.0W 110 KT