ISABEL #15 - DISCUSSION

[AussieMark]

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WTNT43 KNHC 092032
TCDAT3
HURRICANE ISABEL DISCUSSION NUMBER 15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT TUE SEP 09 2003

SATELLITE INTENSITY ESTIMATES FROM ALL THREE AGENCIES REMAIN AT 115
KT. THE EYE HAS BECOME CLOUD-COVERED THIS AFTERNOON...BUT OVER
THE PAST 2 HOURS THE EYE HAS CLEARED OUT AND WARMED SOME. ALSO...
EYEWALL CLOUD TOPS HAVE COOLED SIGNIFICANTLY WITH SOME TOPS AS COLD
AS -80C TO -85C. OBJECTIVE DVORAK T-NUMBERS HAVE ALSO INCREASED TO
115 KT AND SLIGHTLY HIGHER IN THE LAST COUPLE OF HOURS...SO IT IS
POSSIBLE THAT ISABEL HAS STRENGTHENED A LITTLE. HOWEVER...I WOULD
PREFER TO WAIT ANOTHER FEW HOURS TO SEE IF THE EYE CLEARS OUT
BEFORE INCREASING THE INTENSITY.

THE INITIAL MOTION ESTIMATE IS 300/11. ISABEL HAS BEEN MAINTAINING A
STEADY WEST-NORTHWESTWARD MOTION FOR THE PAST 2-3 DAYS AND ALL OF
THE NHC MODEL GUIDANCE HAS HAD A PROFOUND LEFT-OF-TRACK BIAS...
ESPECIALLY THE GFS AND NOGAPS MODELS. THEREFORE...IT IS TIME TO
BAIL OUT ON THE MODEL CONSENSUS AND SHIFT THE FORECAST TRACK CLOSER
TO THE MORE NORTHERN GFDL AND UKMET SOLUTIONS. THE OFFICIAL
FORECAST TRACK IS SIGNIFICANTLY NORTH OF THE PREVIOUS FORECAST
TRACKS...BUT IT WAS NOT SHIFTED AS FAR NORTH AS THE UKMET SOLUTION.
THE MAIN REASON IS THAT THE LARGE MID-/UPPER-LOW JUST NORTH OF THE
LEEWARD ISLANDS HAS BECOME ELONGATED EAST-WEST DURING THE PAST 6
HOURS AND THE FLOW ON THE EAST SIDE OF THE LOW HAS SHIFTED FROM A
SOUTHERLY DIRECTION TO MORE SOUTHEASTERLY. THIS SHOULD IMPART LESS
OF A NORTHWARD COMPONENT TO ISABEL WITH TIME AS THE LOW CONTINUES
MOVE QUICKLY NORTHWESTWARD AND WEAKEN. ON A LARGER SCALE...THE
MID-LATITUDE FLOW OVER NORTH AMERICA IS FORECAST TO AMPLIFY OVER
THE NEXT 5 DAYS WITH A LARGE RIDGE OFF THE U.S. WEST COAST AND A
DEEP TROUGH OVER THE CENTRAL U.S. THE RESULTING PATTERN SHOULD
BUILD AND MAINTAIN A RIDGE ALONG AND EAST OF THE U.S. EAST
COAST...WHICH SHOULD ACT TO KEEP ISABEL MOVING IN A GENERAL
WESTWARD DIRECTION. BY DAY 5...THE STEERING FLOW IS FORECAST TO
WEAKEN AS A WEAK SHORTWAVE TROUGH DEVELOPS OVER THE SOUTHEAAST U.S.
AND ERODES THE RIDGE A LITTLE TO THE NORTHWEST OF ISABEL.

THE UPPER-LEVEL OUTFLOW PATTERN IS FORECAST TO REMAIN VERY FAVORABLE
FOR AT LEAST ANOTHER 48 HOURS...SO SOME ADDITIONAL STRENGTHENING IS
STILL POSSIBLE. GIVEN THAT SATELLITE INTENSITY ESTIMATES ARE
NEARING T6.5...127 KT...SOME INTENSIFICATION IS PROBABLE TONIGHT.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 09/2100Z 20.3N 47.8W 115 KT
12HR VT 10/0600Z 21.1N 49.4W 120 KT
24HR VT 10/1800Z 21.6N 51.4W 125 KT
36HR VT 11/0600Z 21.7N 53.1W 120 KT
48HR VT 11/1800Z 21.8N 54.6W 115 KT
72HR VT 12/1800Z 21.9N 57.5W 115 KT
96HR VT 13/1800Z 22.0N 60.5W 110 KT
120HR VT 14/1800Z 23.0N 64.0W 110 KT