Hurricane IRENE

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HURRICANE IRENE DISCUSSION NUMBER  24
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
500 AM EDT FRI AUG 26 2011

REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE
THAT THE INTENSITY OF IRENE IS NOT QUITE AT MAJOR HURRICANE STATUS.
THE MAXIMUM FLIGHT-LEVEL WINDS AT 700 MB WERE 109 KT ABOUT 75 N MI
EAST-NORTHEAST OF THE CENTER...AND THE MAXIMUM SURFACE WINDS
REPORTED FROM THE STEPPED FREQUENCY MICROWAVE RADIOMETER WERE 87
KT. BASED ON THESE DATA...THE INTENSITY ESTIMATE IS REDUCED TO 95
KT...WHICH IS ALSO BETWEEN THE SATELLITE INTENSITY ESTIMATES OF 102
KT FROM TAFB ANND 90 KT FROM SAB. THE AIRCRAFT DATA INDICATE THAT A
20 N MI WIDE EYE IS PRESENT AND THAT THE CENTRAL PRESSURE REMAINS
NEAR 942 MB.

THE INITIAL MOTION IS NOW 360/12. IRENE IS MOVING THROUGH A WEAKNESS
AT THE WESTERN END OF THE SUBTROPICAL RIDGE...AND IT SHOULD RECURVE
INTO THE WESTERLIES DURING THE FORECAST PERIOD. THE TRACK GUIDANCE
IS TIGHTLY CLUSTERED AROUND A NORTHWARD MOTION DURING THE FIRST 24
HR...FOLLOWED BY A TURN TOWARD THE NORTH-NORTHEAST. THE NEW
FORECAST TRACK CALLS FOR IRENE TO MAKE LANDFALL ALONG THE NORTH
CAROLINA OUTER BANKS IN ABOUT 36 HR...THEN PASS NEAR THE COAST OF
THE MID-ATLANTIC STATES BEFORE MAKING LANDFALL IN NEW ENGLAND IN
ROUGHLY 60 HOURS. THERE HAS BEEN NO SIGNIFICANT CHANGE IN THE TRACK
GUIDANCE SINCE THE LAST ADVISORY... AND WHILE THE FORECAST TRACK
HAS BEEN ADJUSTED SLIGHTLY TO THE EAST THIS SHOULD BE CONSIDERED A
NOISE-LEVEL CHANGE. AFTER LANDFALL... IRENE SHOULD MERGE WITH THE
CORE OF THE WESTERLIES AND TURN NORTHEASTWARD WITH ACCELERATION.

WATER VAPOR IMAGERY AND ANALSYES FROM CIMSS AT THE UNIVERSITY OF
WISCONSIN SUGGEST THAT IRENE IS ENCOUNTERING LIGHT TO MODERATE
SOUTHWESTERLY VERTICAL WIND SHEAR.  THIS...ALONG WITH THE CURRENT
CYCLONE STRUCTURE AND DRY AIR ADVECTING TOWARD THE HURRICANE IN
WATER VAPOR IMAGERY...ARGUE AGAINST SIGNIFICANT STRENGTHENING....
AND INDEED THE INTENSITY GUIDANCE SHOWS LITTLE CHANGE IN STRENGTH 
BEFORE LANDFALL.  ON THE OTHER HAND...THE EYEWALL CONVECTION IS
CURRENTLY STRONG...AND THE SEA SURFACE TEMPERATURES ALONG THE
FORECAST TRACK ARE 28-29C.  THIS SUGGESTS SOME MODEST STRENGTHENING
IS POSSIBLE.  IRENE IS EXPECTED TO BE NEAR THE CATEGORY 2/3
BOUNDARY WHEN IT REACHES THE VICINITY OF THE OUTER BANKS...AND
SLOWLY WEAKEN AFTER THAT. AFTER MOVING INTO NEW ENGLAND...IRENE
SHOULD WEAKEN QUICKLY AS IT UNDERGOES EXTRATROPICAL TRANSITION.

IRENE REMAINS A VERY LARGE TROPICAL CYCLONE.  THE WIND RADII HAVE
BEEN ADJUSTED BASED ON AIRCRAFT DATA AND AN ASCAT OVERPASS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/0900Z 29.3N  77.2W   95 KT 110 MPH
 12H  26/1800Z 31.0N  77.2W  100 KT 115 MPH
 24H  27/0600Z 33.1N  76.9W  100 KT 115 MPH
 36H  27/1800Z 35.3N  76.1W  105 KT 120 MPH
 48H  28/0600Z 37.8N  75.0W   85 KT 100 MPH
 72H  29/0600Z 45.0N  70.4W   55 KT  65 MPH...INLAND
 96H  30/0600Z 53.0N  61.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  31/0600Z 58.5N  44.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BEVEN
 
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