[Tropical] Tropical Cyclone Discussion

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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


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