128
WTNT44 KNHC 052034
TCDAT4
TROPICAL STORM GRACE DISCUSSION NUMBER 4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092009
500 PM AST MON OCT 05 2009
GRACE CONTINUES TO HAVE THE SATELLITE APPEARANCE OF A TROPICAL
CYCLONE AND A MODERATE TO DEEP WARM CORE AS INDICATED BY RECENT
AMSU PASSES. HOWEVER...CLOUD TOP TEMPERATURES HAVE CONTINUED TO
WARM OVER THE PAST FEW HOURS AS THE CYCLONE IS NOW OVER SSTS OF
17-18C. THE INTENSITY IS DECREASED TO 50 KT BASED A SUBTROPICAL
CLASSIFICATION OF 3.5 FROM TAFB AND A DVORAK CI-NUMBER OF 3.0 FROM
SAB. A QUIKSCAT PASS SHOULD PROVIDE SOME INFORMATION ON THE
INTENSITY AND STRUCTURE OF GRACE SOON. THE CENTRAL PRESSURE IS HELD
AT 990 MB BASED ON AN 1800 UTC OBSERVATION OF 992 MB AND A WIND OF
20 KT FROM SHIP A8I02 ABOUT 30 NM NORTH OF THE CENTER OF GRACE.
THE INITIAL MOTION ESTIMATE IS 025/26 KT...AS GRACE IS BEING STEERED
BY DEEP-LAYER SOUTHWESTERLY FLOW AHEAD OF A MID- TO UPPER-LEVEL
TROUGH ALONG 27W. BY TUESDAY MORNING...ALL OF THE GLOBAL MODELS
SHOW GRACE BEING ABSORBED BY A FRONT ASSOCIATED WITH A DEEPENING
EXTRATROPICAL CYCLONE TO THE NORTHWEST OF THE BRITISH ISLES.
IT IS WORTH NOTING THAT OTHER ATLANTIC TROPICAL STORMS HAVE FORMED
FARTHER NORTH THAN GRACE DID. IN 2008 TROPICAL STORM LAURA WAS
FIRST CLASSIFIED AS A TROPICAL STORM AT 40.6N....SLIGHTLY FARTHER
NORTH THAN THE LATITUDE OF 40.2N WHERE GRACE WAS FIRST CLASSIFIED
AS A TROPICAL STORM AT 0000 UTC TODAY. ALSO...IT IS LIKELY THAT
POST-STORM ANALYSIS WILL SHOW GRACE BECOMING A TROPICAL STORM
EARLIER...AND FARTHER SOUTH...THAN INDICATED OPERATIONALLY.
FORECAST POSITIONS AND MAX WINDS
INITIAL 05/2100Z 47.7N 14.8W 50 KT
12HR VT 06/0600Z 50.6N 12.0W 50 KT
24HR VT 06/1800Z...DISSIPATED
FORECASTER BRENNAN
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