069
WTNT44 KNHC 050236
TCDAT4
TROPICAL STORM GRACE DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092009
1100 PM AST SUN OCT 04 2009
CONVECTIVE ACTIVITY ASSOCIATED WITH THE LOW PRESSURE AREA NORTHEAST
OF THE AZORES ISLANDS HAS BECOME BETTER ORGANIZED THIS EVENING. THE
CONVECTION...WHICH HAS SHOWN SOME ORGANIZATION FOR MUCH OF THE
DAY...IS RELATIVELY DEEP AND SURROUNDS AN EYE-LIKE FEATURE THAT HAS
PERSISTED FOR SEVERAL HOURS. THIS IS THE SAME SURFACE LOW PRESSURE
AREA THAT MOVED THROUGH THE AZORES SEVERAL DAYS AGO AND MADE A
COUNTER-CLOCKWISE LOOP. THE LOW...PREVIOUSLY ASSOCIATED WITH AN
OCCLUDED FRONT AND CO-LOCATED WITH AN UPPER LOW...HAS SINCE LOST
ITS FRONTAL STRUCTURE AND IS NOW LOCATED UNDER A FAIRLY UNIFORM
SOUTHWESTERLY UPPER FLOW. IN ADDITION...2210Z ASCAT DATA INDICATED A
VERY SMALL RADIUS OF MAXIMUM WIND...LESS THAN 20 MILES. WITH THESE
STRUCTURAL CHANGES...THE SYSTEM CAN NOW BE CLASSIFIED AS A TROPICAL
STORM.
THE ASCAT PASS SHOWED A COUPLE OF 45-50 KT WIND VECTORS TO THE
SOUTHEAST OF THE CENTER...AND THESE DATA ARE THE BASIS FOR THE 55
KT INITIAL INTENSITY. GRACE IS CURRENTLY OVER SSTS AROUND 21
DEGREES CELSIUS AND WITHIN AN UPPER-LEVEL ENVIRONMENT CHARACTERIZED
BY LIGHT TO MODERATE SOUTHWESTERLY SHEAR. ALTHOUGH THE SHEAR IS NOT
FORECAST TO INCREASE DURING THE NEXT DAY OR TWO...THE CYCLONE IS
HEADED FOR EVEN COLDER WATER AND WILL LIKELY BEGIN TO WEAKEN VERY
SOON. THE GLOBAL MODELS SUGGEST THAT THE SMALL CYCLONE WILL BE
ABSORBED BY A LARGER EXTRATROPICAL CYCLONE OVER THE NORTHEASTERN
ATLANTIC IN ABOUT 36 HOURS...IF NOT SOONER.
GRACE IS MOVING NORTHEASTWARD IN THE DEEP LAYER SOUTHWESTERLY FLOW
OVER THE NORTHEASTERN ATLANTIC. A GENERAL NORTHEASTWARD MOTION IS
EXPECTED TO CONTINUE UNTIL DISSIPATION.
FORECAST POSITIONS AND MAX WINDS
INITIAL 05/0300Z 41.2N 20.3W 55 KT
12HR VT 05/1200Z 44.0N 18.0W 50 KT
24HR VT 06/0000Z 48.0N 16.0W 45 KT
36HR VT 06/1200Z...DISSIPATED
FORECASTER BROWN/FRANKLIN
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