[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 171440
TCDAT4
HURRICANE IRENE DISCUSSION NUMBER  52
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT WED AUG 17 2005

THE OVERALL CLOUD PATTERN OF IRENE IS BEGINNING TO DETERIORATE
AND IS NOW EXPERIENCING WESTERLY SHEAR. AN AVERAGE OF THE DATA T AND
CURRENT INTENSITY NUMBERS FROM BOTH TAFB AND SAB WARRANTS BRINGING
DOWN THE INITIAL INTENSITY TO 65 KT. THE INITIAL 34 AND 50 KNOT
WIND RADII HAVE BEEN ADJUSTED BASED ON A 0935 UTC HIGH RESOLUTION
QUIKSCAT PASS.

THE INITIAL MOTION ESTIMATE IS A SLIGHTLY FASTER 070/10...AND
INDICATES SOME ACCELERATION OVER THE PREVIOUS AVERAGE 6 HOUR MOTION
OF 080/8. WATER VAPOR IMAGERY INDICATES A VIGOROUS SHORTWAVE TROUGH
HAS MOVED OFF THE MID-ATLANTIC AND NORTHEASTERN U.S. COASTS AND IS
SWEEPING RAPIDLY TOWARD IRENE. THIS SAME FEATURE HAS ALSO
INTRODUCED THE STRONG WESTERLY MID-TO UPPER-LEVEL SHEAR ON THE
SYSTEM. AS THE SHORTWAVE TROUGH AND ASSOCIATED SURFACE FRONT
APPROACH IRENE FROM THE WEST...THE HURRICANE IS EXPECTED TO QUICKLY
ACCELERATE TO THE NORTHEAST IN RESPONSE TO THE INCREASING
SOUTHWESTERLY STEERING FLOW. IRENE IS FORECAST TO MOVE OVER SHARPLY
LOWER SSTS WITHIN 24 HOURS...NORTH OF 41N LATITUDE...THE CYCLONE
SHOULD QUICKLY DECOUPLE AND BECOME AN EXTRATROPICAL LOW. SINCE THE
CYCLONE HAS BEEN CONSISTENTLY SOUTH OF OUR FORECAST TRACK THE
EXTRA-TROPICAL TRANSITION HAS BEEN DELAYED TO 36 HOURS. THIS MAY BE
SOMEWHAT GENEROUS. BEYOND THAT TIME...EXTRATROPICAL IRENE SHOULD
HOOK UP WITH THE MID-LATITUDE WESTERLIES AND RACE OFF TO THE
NORTHEAST TOWARD GREENLAND AND ICELAND. THE OFFICIAL TRACK IS
SIMILAR TO THE PREVIOUS FORECAST AND IS GOOD AGREEMENT OF THE
CONSENSUS OF THE TIGHTLY PACKED NHC MODEL GUIDANCE.

ALTHOUGH IRENE IS EXPECTED TO REMAIN OVER 27-28C SSTS FOR ANOTHER
18-24 HOURS OR SO...THE VERTICAL SHEAR IS FORECAST TO GRADUALLY
INCREASE AND IRENE IS EXPECTED TO WEAKEN TO A TROPICAL STORM IN 12
HOURS. ONCE IRENE MOVES NORTH OF 41N...THE MUCH COLDER WATER AND
STRONG SOUTHWESTERLY SHEAR OF 30-35 KT SHOULD BRING ABOUT A
TRANSITION TO AN EXTRATROPICAL CYCLONE. AFTER 48 HOURS...IRENE IS
EXPECTED TO BECOME ABSORBED BY A LARGER EXTRATROPICAL LOW. THE
OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND
THE SHIPS INTENSITY MODEL.

FORECASTER COBB/PASCH

FORECAST POSITIONS AND MAX WINDS

INITIAL      17/1500Z 37.1N  58.6W    65 KT
 12HR VT     18/0000Z 38.8N  55.6W    60 KT
 24HR VT     18/1200Z 43.0N  50.5W    55 KT
 36HR VT     19/0000Z 50.5N  44.0W    50 KT...EXTRATROPICAL
 48HR VT     19/1200Z 59.5N  36.0W    50 KT...EXTRATROPICAL
 72HR VT     20/1200Z...DISSIPATED

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