ISABEL #5 - DISCUSSION

[AussieMark]

000
WTNT43 KNHC 070846
TCDAT3
TROPICAL STORM ISABEL DISCUSSION NUMBER 5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT SUN SEP 07 2003

OVERNIGHT SATELLITE IMAGERY SHOWS THAT ISABEL CONTINUES TO EXHIBIT A
WELL-DEFINED CURVED CONVECTIVE BAND...AND THE LAST FEW IMAGES
SUGGEST THAT THE CONVECTION HAS BEGUN TO WRAP CLOSER TO THE CENTER.
SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS 55 KT FROM
TAFB...SAB...AND AFWA. THEREFORE...THE INITIAL INTENSITY IS RAISED
TO 55 KT FOR THIS ADVISORY. GLOBAL MODELS SUGGEST THAT A MID/UPPER
LEVEL RIDGE WILL REMAIN NORTH OF THE CYCLONE THROUGH THE FORECAST
PERIOD...PROVIDING FAVORABLE CONDITIONS FOR STRENGTHENING. THE
SHIPS MODEL TAKES ISABEL TO 85 KT IN 72 HOURS...AND THE GFDL BRINGS
THE INTENSITY UP TO 95 KT IN 48 HOURS. THE INTENSITY FORECAST WILL
BE RATHER CONSERVATIVE AND INDICATE GRADUAL STRENGTHENING OVER THE
NEXT 2-3 DAYS...WITH THE INTENSITY LEVELING OFF AT 85 KT BY 72
HOURS WHICH IS IN GENERAL AGREEMENT WITH SHIPS.

THE INITIAL MOTION IS 275/09...SLIGHTLY NORTH OF THE PREVIOUS
ADVISORY. THE SYNOPTIC PATTERN REMAINS BASICALLY UNCHANGED FROM
THE PREVIOUS FORECAST...WITH ISABEL BEING STEERED BY A MID/UPPER
LEVEL RIDGE TO THE NORTH. WATER VAPOR IMAGERY INDICATES AN
UPPER-LEVEL TROUGH ABOUT 900 NM NORTHWEST OF THE TROPICAL CYCLONE.
LARGE-SCALE GLOBAL MODELS SUGGEST THAT THIS TROUGH WILL CREATE JUST
ENOUGH OF A WEAKNESS IN THE RIDGE TO ALLOW FOR A MORE
WEST-NORTHWEST MOTION BEYOND 12 HOURS...AND CONTINUE THAT MOTION
THROUGH DAY 5. NHC TRACK GUIDANCE BASICALLY FOLLOWS THIS
SCENARIO...WITH THE FORECAST TRACK ADJUSTED A TAD TO THE NORTH OF
THE PREVIOUS TRACK AND REMAINING ON THE SOUTH SIDE OF THE GUIDANCE.

FORECASTER MOLLEDA/LAWRENCE

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/0900Z 13.7N 37.1W 55 KT
12HR VT 07/1800Z 13.8N 38.5W 60 KT
24HR VT 08/0600Z 14.8N 40.9W 65 KT
36HR VT 08/1800Z 15.6N 43.2W 70 KT
48HR VT 09/0600Z 16.5N 45.3W 75 KT
72HR VT 10/0600Z 18.0N 50.0W 85 KT
96HR VT 11/0600Z 18.5N 55.5W 85 KT
120HR VT 12/0600Z 19.0N 60.0W 85 KT