000 WTNT44 KNHC 260900 TCDAT4 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