[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT44 KNHC 160831
TCDAT4
HURRICANE IRENE DISCUSSION NUMBER  47
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT TUE AUG 16 2005

WHILE THE OVERALL CONVECTIVE CLOUD APPEARANCE HAS CHANGED LITTLE
DURING THE PAST 6 HOURS IN INFRARED SATELLITE IMAGERY...SEVERAL
SSSMI...AMSU...AND TRMM MICROWAVE OVERPASSES HAVE SHOWN A GRADUAL
DEGRADATION IN THE INNER CORE CONVECTIVE FEATURES AND EYE
STRUCTURE. A DISTINCT EASTWARD TILT OF THE EYE WAS NOTED IN 0447Z
AND 0625Z TRMM OVERPASSES...ALTHOUGH THE LATTER IMAGE SUGGESTED
THAT LESS TILTING OF THE EYE WAS OCCURRING AS COMPARED TO EARLIER
PASSES. SATELLITE INTENSITY ESTIMATES ARE T4.5/77KT FROM BOTH TAFB
AND SAB. GIVEN THE RAGGED EYE APPEARANCE NOTED IN THE MICROWAVE
DATA...THE INITIAL INTENSITY HAS BEEN DECREASED TO 75 KT.

THE INITIAL MOTION ESTIMATE IS 090/08 BASED ON THE LAST 6 HOURS OF
MICROWAVE SATELLITE POSITIONS. THE EASTWARD MOTION IS LIKELY DUE TO
A SHORTWAVE CAUGHT UP IN THE FASTER WESTERLIES WELL TO THE NORTH OF
IRENE THAT IS BYPASSING THE CYCLONE. THIS HAS RESULTED IN WEAKER
WESTERLY STEERING FLOW ON THE SOUTH SIDE OF AN EAST-WEST ORIENTED
JETSTREAM. HOWEVER...A MUCH STRONGER AND HIGHER AMPLITUDE SHORTWAVE
TROUGH OVER THE EASTERN GREAT LAKES AND OHIO VALLEY REGION IS
EXPECTED TO MOVE QUICKLY EASTWARD AND GRADUALLY LIFT OUT IRENE TO
THE NORTHEAST BY 36 HOURS...AND THEN RAPIDLY ACCELERATE THE CYCLONE
BY 48 HOURS. BETWEEN 36-48 HOURS...IRENE WILL BE MOVING OVER
SUB-24C SSTS...SO TRANSITION TO A POWERFUL EXTRATROPICAL LOW
PRESSURE SYSTEM IS EXPECTED. DUE TO THE MORE EASTWARD INITIAL
POSITION...THE OFFICIAL FORECAST TRACK IS A LITTLE TO THE RIGHT OF
THE PREVIOUS FORECAST...AND IS CLOSE TO THE NHC MODEL CONSENSUS.

THE INITIAL EASTWARD MOTION WILL KEEP IRENE OVER WARMER WATER A
LITTLE LONGER THAN PREVIOUSLY EXPECTED...BUT A GRADUAL INCREASE IN
THE WESTERLY VERTICAL SHEAR WILL LIKELY OVERCOME ANY POSITIVE
CONTRIBUTION FROM THE 28C SSTS. ONCE IRENE HITS THE ICY WATERS OF
THE NORTH ATLANTIC IN ABOUT 48 HOURS...ANY REMAINING TROPICAL
CHARACTERISTICS SHOULD QUICKLY DISAPPEAR. HOWEVER...WITH SUCH A
STRONG SHORTWAVE TROUGH AND JETSTREAM APPROACHING...THE INCREASING
BAROCLINIC ENERGY SHOULD KEEP IRENE A RATHER POTENT EXTRATROPICAL
LOW PRESSURE SYSTEM OVER THE FAR NORTH ATLANTIC.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      16/0900Z 36.7N  63.5W    75 KT
 12HR VT     16/1800Z 36.9N  62.0W    70 KT
 24HR VT     17/0600Z 37.8N  60.1W    65 KT
 36HR VT     17/1800Z 39.8N  56.7W    55 KT...BECOMING EXTRATROPICAL
 48HR VT     18/0600Z 44.6N  50.1W    50 KT...EXTRATROPICAL
 72HR VT     19/0600Z 53.6N  37.8W    45 KT...EXTRATROPICAL
 96HR VT     20/0600Z 59.0N  31.0W    45 KT...EXTRATROPICAL
120HR VT     21/0600Z...ABSORBED BY FRONTAL SYSTEM

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