[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 172030
TCDAT4
TROPICAL STORM IRENE DISCUSSION NUMBER  53
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT WED AUG 17 2005

THE STRONG WESTERLY SHEAR HAS TAKEN ITS TOLL ON IRENE AND THE
SYSTEM IS NO LONGER A HURRICANE. AN AVERAGE OF DVORAK NUMBERS FROM
THE THREE SATELLITE AGENCIES ALSO SUPPORTS LOWERING THE INTENSITY
TO 60 KT FOR THIS ADVISORY.

THE INITIAL MOTION ESTIMATE HAS PICKED UP TO 050/18...INDICATING
THAT THE ACCELERATION OF THE SYSTEM CONTINUES. WATER VAPOR IMAGERY
SHOWS A VIGOROUS SHORTWAVE TROUGH EXTENDING FROM THE CANADIAN
MARITIMES TO 28N68W THAT IS MOVING RAPIDLY TOWARD IRENE. AS THIS
SHORTWAVE TROUGH AND ASSOCIATED SURFACE FRONT SWEEPS OVER IRENE
FROM THE WEST...THE STORM IS EXPECTED TO ACCELERATE FURTHER
TO THE NORTHEAST IN RESPONSE TO THE INCREASING SOUTHWESTERLY
STEERING FLOW. IRENE IS FORECAST TO MOVE OVER SHARPLY LOWER SSTS
WITHIN 12 HOURS...NORTH OF 41N LATITUDE. THE CYCLONE SHOULD QUICKLY
DECOUPLE OVER THE COOLER WATERS AND BECOME AN EXTRATROPICAL STORM
BY 24 HOURS...OR SOONER...AS INDICATED BY THE FSU CYCLONE PHASE
ANALYSIS WEB PAGE. BEYOND 24 HOURS...EXTRATROPICAL IRENE SHOULD
CONTINUE ACCELERATING IN THE MID-LATITUDE WESTERLIES AND RACE
OFF TO THE NORTHEAST TOWARD GREENLAND AND ICELAND. THE OFFICIAL
TRACK IS VIRTUALLY IDENTICAL TO THE PREVIOUS FORECAST AND IS GOOD
AGREEMENT WITH THE CONSENSUS OF THE TIGHTLY PACKED NHC MODEL
GUIDANCE.

THE INITIAL 12 FOOT SEA RADII HAVE BEEN EXPANDED OUT TO
200 NM IN THE NE QUADRANT BASED ON A SHIP REPORT FROM VESSEL
ELVX2.

FORECASTER COBB/PASCH

FORECAST POSITIONS AND MAX WINDS

INITIAL      17/2100Z 38.5N  56.3W    60 KT
 12HR VT     18/0600Z 41.1N  52.9W    55 KT
 24HR VT     18/1800Z 47.1N  46.9W    50 KT...EXTRATROPICAL
 36HR VT     19/0600Z 55.5N  40.5W    50 KT...EXTRATROPICAL
 48HR VT     19/1800Z...ABSORBED

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