000
WTNT44 KNHC 270258
TCDAT4
HURRICANE IRENE DISCUSSION NUMBER 27
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
1100 PM EDT FRI AUG 26 2011
AIR FORCE AND NOAA HURRICANE HUNTER AIRCRAFT LATE THIS AFTERNOON AND EARLY EVENING HAVE FOUND SURFACE PRESSURES OF 950-951 MB AND FLIGHT-LEVEL WINDS RANGING FROM 99 KT TO 108 KT IN THE SOUTHEAST QUADRANT OF IRENE. HOWEVER...SFMR SURFACE WINDS HAVE BEEN MUCH LOWER THAN THE STANDARD 90 PERCENT REDUCTION FACTOR TYPICALLY YIELDS. THIS DISPARITY IS LIKELY DUE TO THE LACK OF SIGNIFICANT CONVECTION OVER THE SOUTHERN SEMICIRCLE. NOAA DOPPLER RADAR DATA FROM WILMINGTON AND MOREHEAD CITY HAVE BEEN INDICATING VIGOROUS CONVECTION REDEVELOPING NORTH AND EAST OF THE RAGGED EYE...WITH DOPPLER VELOCITIES OF 90 KT OR GREATER AT ALTITUDE ABOVE 15000 FEET. BASED ON THE RADAR DATA AND THE POSSIBILITY THAT THE STRONGER FLIGHT-LEVEL WINDS COULD EVENTUALLY WORK INTO NORTHEAST QUADRANT OF IRENE...THE INITIAL INTENSITY IS BEING HELD AT 85 KT.
RADAR AND RECON FIXES INDICATE IRENE HAS MADE THE LONG-FORECAST TURN TOWARD THE NORTH-NORTHEAST NOW AND IS MOVING AT 020/12 KT. IRENE IS CAUGHT BETWEEN A BROAD SUBTROPICAL RIDGE TO THE EAST AND AN APPROACHING SHORTWAVE TROUGH CURRENTLY MOVING EASTWARD OVER THE GREAT LAKES AND OHIO VALLEY. THE HURRICANE IS EXPECTED TO CONTINUE MOVING NORTH-NORTHEASTWARD FOR THE NEXT 24 HOURS OR SO AS THE RIDGE TO THE EAST AMPLIFIES NORTHWARD. THEREAFTER...THE CYCLONE SHOULD ACCELERATE TO THE NORTHEAST AS IT GETS CAUGHT UP IN DEEP-LAYER SOUTHWESTERLY FLOW AHEAD OF THE SHORTWAVE TROUGH. THE FORECAST TRACK HAS ONLY BEEN NUDGED SLIGHTLY EASTWARD OF THE PREVIOUS TRACK THROUGH 36 HOURS DUE TO THE MORE EASTWARD INITIAL POSITION. HOWEVER...ALL OF THE MODELS SUGGEST THAT SOME SLIGHT MID-LEVEL RIDGING WILL OCCUR ACROSS SOUTHERN NEW ENGLAND AND THE MID-ATLANTIC STATES DURING THE NEXT 12-24 HOURS...WHICH SHOULD ACT TO KEEP IRENE CLOSE TO THE COASTS OF NEW JERSEY AND THE DELMARVA PENINSULA. THE TRACK FORECAST LIES DOWN THE MIDDLE OF THE NHC GUIDANCE ENVELOPE AND IS A BLEND OF THE GFS AND ECMWF MODEL TRACKS.
IRENE IS EXPECTED TO REMAIN OVER SSTS GREATER THAN 28C UNTIL LANDFALL ALONG THE NORTH CAROLINA OUTER BANKS IN 12-18 HOURS. THIS SHOULD ALLOW THE CYCLONE TO MAINTAIN ITS CURRENT INTENSITY OR ONLY WEAKEN SLIGHTLY. AFTER LANDFALL...HOWEVER...LAND INTERACTION... COOLER WATER...AND GRADUALLY INCREASING SOUTHWESTERLY VERTICAL WIND SHEAR IS EXPECTED TO INDUCE STEADY WEAKENING. ALTHOUGH A STATIONARY FRONT CURRENTLY LIES ACROSS SOUTHERN NEW ENGLAND...THIS FEATURE IS EXPECTED TO LIFT NORTHWARD DUE TO THE VERY LARGE CIRCULATION OF IRENE. THIS SHOULD DELAY EXTRATROPICAL TRANSITION UNTIL IRENE IS OVER MAINE OR SOUTHEASTERN CANADA.
FORECAST POSITIONS AND MAX WINDS
INIT 27/0300Z 32.6N 76.9W 85 KT 100 MPH
12H 27/1200Z 34.2N 76.4W 80 KT 90 MPH
24H 28/0000Z 36.7N 75.5W 75 KT 85 MPH
36H 28/1200Z 39.8N 74.0W 70 KT 80 MPH
48H 29/0000Z 43.8N 71.3W 60 KT 70 MPH...INLAND
72H 30/0000Z 52.0N 62.0W 45 KT 50 MPH...POST-TROP/EXTRATROP
96H 31/0000Z 56.5N 46.0W 40 KT 45 MPH...POST-TROP/EXTRATROP
120H 01/0000Z 57.5N 26.0W 35 KT 40 MPH...POST-TROP/EXTRATROP
$$
FORECASTER STEWART
