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.