000 WTNT44 KNHC 280257 TCDAT4 HURRICANE IRENE DISCUSSION NUMBER 31 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011 1100 PM EDT SAT AUG 27 2011 IRENE HAS CHANGED LITTLE IN APPEARANCE IN SATELLITE IMAGERY...BUT THE RADAR DEPICTION HAS DEGRADED OVER THE PAST FEW HOURS. AN AIR FORCE RECONNAISSANCE AIRCRAFT INVESTIGATING THE HURRICANE THIS EVENING HAS FOUND 700 MB FLIGHT-LEVEL WINDS OF 92 KT AND SFMR WINDS OF 66 KT IN A SMALL AREA MORE THAN 100 NMI EAST OF THE CENTER. BASED ON THIS INFORMATION...THE INTENSITY OF IRENE IS BEING MAINTAINED AT 70 KT FOR THIS ADVISORY. IT SHOULD BE NOTED THAT THE WIND FIELD GRAPHICS BASED ON THE FOUR-QUADRANT RADII WILL DEPICT AN UNREALISTICALLY LARGE AREA OF HURRICANE-FORCE WINDS. THE INITIAL MOTION ESTIMATE IS NOW 020/14...AND IRENE REMAINS ON TRACK. IRENE IS EXPECTED TO CONTINUE MOVING NORTH-NORTHEASTWARD AHEAD OF AN EASTWARD-MOVING SHORTWAVE TROUGH...AND SKIRT THE MID-ATLANTIC COAST TONIGHT AND EARLY SUNDAY MORNING...AND MOVE OVER NEW ENGLAND BY SUNDAY AFTERNOON. AFTER IRENE BECOMES A POST-TROPICAL/EXTRATROPICAL LOW BY 36 HOURS...THE CYCLONE SHOULD GRADUALLY TURN NORTHEASTWARD THEN EAST-NORTHEASTWARD AS IT MOVES INTO THE DEEP-LAYER MID-LATITUDE WESTERLIES. THE FORECAST TRACK IS JUST AN EXTENSION OF THE PREVIOUS ADVISORY AND REMAINS IN THE MIDDLE OF THE TIGHTLY PACKED NHC MODEL GUIDANCE. IRENE WILL BE MOVING OVER PROGRESSIVELY COOLER WATER UNTIL LANDFALL OCCURS ON LONG ISLAND...WHICH WOULD NORMALLY RESULT IN SIGNIFICANT WEAKENING OF MOST HURRICANES. HOWEVER...DUE TO THE UNUSUALLY LARGE WIND FIELD OF IRENE...ONLY SLOW WEAKENING IS EXPECTED THROUGHOUT THE FORECAST PERIOD...AND IT WILL ONLY TAKE MODEST CONVECTION TO BRING DOWN STRONGER WINDS ALOFT TO THE SURFACE AS SUSTAINED HURRICANE-FORCE WINDS OR GUSTS. MORE SO THAN WITH MOST STORMS...THE WINDS WITH IRENE INCREASE SHARPLY WITH HEIGHT ABOVE THE SURFACE. AS IRENE MOVES THROUGH AREAS WITH HIGH-RISE STRUCTURES...THESE BUILDINGS COULD EXPERIENCE WINDS SIGNIFICANTLY STRONGER THAN THE SURFACE WINDS. WINDS AT THE 30-STORY LEVEL WILL LIKELY BE 20 PERCENT HIGHER THAN AT THE SURFACE...AND WINDS 80-100 STORIES UP COULD BE ABOUT 30 PERCENT HIGHER THAN AT THE SURFACE. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 37.3N 75.4W 70 KT 80 MPH 12H 28/1200Z 39.8N 74.1W 65 KT 75 MPH 24H 29/0000Z 44.0N 71.8W 55 KT 65 MPH...INLAND 36H 29/1200Z 48.5N 67.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 30/0000Z 52.4N 62.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 31/0000Z 57.7N 48.6W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 01/0000Z 60.0N 33.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 02/0000Z 61.2N 24.5W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ FORECASTER STEWART