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TROPICAL STORM GABRIELLE DISCUSSION NUMBER 29
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT TUE SEP 18 2001
DEEP CONVECTION HAS PERSISTED NORTH AND WEST OF THE LOW-LEVEL
CIRCULATION CENTER. HOWEVER...THE APPEARANCE OF THIS SYSTEM IS MORE
INDICATIVE OF AN EXTRATROPICAL LOW. THE INITIAL INTENSITY IS
INCREASED TO 60 KTS BASED PRIMARILY ON AN OBSERVATION FROM SHIP WMLH
LOCATED ABOUT 90 NM NW OF THE CENTER. THE SHIP REPORTED 984.5 MB
PRESSURE...75F AIR TEMPERATURE...72F DEWPOINT. THIS DATA COUPLED
WITH AMSU DATA STILL INDICATES THAT GABRIELLE REMAINS A WARM CORE
SYSTEM...WHICH JUSTIFIES MAINTAINING IT AS A TROPICAL STORM FOR THIS
ADVISORY.
INITIAL MOTION ESTIMATE IS 045/16. THERE REMAINS LITTLE CHANGE IN
THE PREVIOUS FORECAST TRACK OR REASONING. GABRIELLE IS EXPECTED TO
ACCELERATE NORTHEASTWARD THROUGH THE FORECAST PERIOD AS STRONG
WESTERLY MID-LATITUDE FLOW BEGINS TO AFFECT THE SYSTEM IN 12-24
HOURS. THIS SCENARIO IS SUPPORTED BY ALL OF THE GLOBAL MODELS...
WHICH REMAIN IN EXCELLENT AGREEMENT ON KEEPING THE CENTER OF
GABRIELLE OFF THE NEWFOUNDLAND COAST THROUGH 48 HOURS.
THE GLOBAL MODELS ARE INDICATING SOME ADDITIONAL INTENSIFICATION
WITH THIS SYSTEM IN 12 TO 24 HOURS AS IT TRANSITIONS TO AN
EXTRATROPICAL LOW. IN FACT THE INTENSITY FORECAST IS INCREASED FROM
THE EARLIER ADVISORY...ACCOUNTING FOR THE GLOBAL MODELS TREND IN
DEVELOPING A STRONGER SYSTEM. HOWEVER...GABRIELLE SHOULD QUICKLY
BECOME EXTRATROPICAL ONCE THE SYSTEM PASSES NORTH OF 43N LATITUDE
WHERE WATER TEMPERATURES DROP BELOW 20C.
FORECASTER STEWART/HOLWEG
FORECAST POSITIONS AND MAX WINDS
INITIAL 18/2100Z 40.6N 58.4W 60 KTS...BECOMING EXTRATROPICAL
12HR VT 19/0600Z 42.4N 55.9W 60 KTS...EXTRATROPICAL
24HR VT 19/1800Z 44.9N 52.1W 60 KTS...EXTRATROPICAL
36HR VT 20/0600Z 47.3N 47.7W 60 KTS...EXTRATROPICAL
48HR VT 20/1800Z 49.3N 42.2W 60 KTS...EXTRATROPICAL
72HR VT 21/1800Z 51.0N 33.5W 55 KTS...EXTRATROPICAL
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