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HURRICANE IRENE DISCUSSION NUMBER 12

Published on August 23, 2011 10:02 AM | Comments

This was the 5 AM update:


HURRICANE IRENE DISCUSSION NUMBER 12
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
500 AM EDT TUE AUG 23 2011

SMOOTHING THROUGH ALL OF THE AIRCRAFT FIXES SINCE IRENE MOVED OFF
THE COAST OF PUERTO RICO MORE THAN 18 HOURS AGO YIELDS A LONG TERM
MOTION OF 295/10 KT...WHICH IS USED FOR THIS ADVISORY. THERE IS NO
SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK REASONING. THE
23/00Z G-IV JET AIRCRAFT AND AIR FORCE C-130 DROPSONDE DATA APPEAR
TO HAVE SETTLED DOWN THE MODELS...AND THERE IS CONSIDERABLY LESS
DIFFERENCE AMONG THE VARIOUS MODEL SOLUTIONS NOW. THE OVERWHELMING
CONSENSUS IS THAT IRENE WILL GRADUALLY TURN NORTHWESTWARD OVER THE
NEXT 2-3 DAYS AND THEN MOVE NORTHWARD THROUGH A DEVELOPING BREAK IN
THE SUBTROPICAL RIDGE OVER THE SOUTHEASTERN UNITED STATES. THE
OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND
LIES VERY CLOSE TO CONSENSUS MODELS TVCN AND TVCA.

AN EARLIER RECON FLIGHT INDICATED THE PRESSURE HAD ONLY FALLEN BY 2
MB DOWN TO 978 MB...AND THE OVERALL APPEARANCE IN SATELLITE IMAGERY
HAS CHANGED LITTLE SINCE THE PREVIOUS ADVISORY. AS A RESULT...THE
INITIAL INTENSITY IS BEING HELD AT 85 KT...WHICH COULD BE GENEROUS.
IRENE IS FORECAST TO REMAIN IN A RELATIVELY LOW VERTICAL WIND SHEAR
ENVIRONMENT AND OVER SSTS NEAR 30C. THAT COMBINATION...ALONG WITH
EXPANDING OUTFLOW IN ALL QUADRANTS...SHOULD ALLOW FOR IRENE TO
BECOME A MAJOR HURRICANE WITHIN THE NEXT 24 HOURS ONCE THE CYCLONE
CLEARS THE EFFECTS OF HISPANIOLA...AND PROBABLY MAINTAIN MAJOR
HURRICANE STATUS THROUGHOUT THE REMAINDER OF THE 5-DAY FORECAST
PERIOD. THE INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY
AND CLOSELY FOLLOWS A BLEND OF THE HWRF AND GFDL MODEL INTENSITY
FORECASTS...AND CONVERSION OF THE SURFACE PRESSURES DEPICTED IN THE
GFS AND ECMWF MODELS.

WIND RADII WERE EXPANDED BASED ON A BLEND OF RECON FLIGHT-LEVEL
WINDS...SFMR WINDS...AND SURFACE OBSERVATIONS.

IRENE IS FORECAST TO BECOME A LARGER THAN AVERAGE HURRICANE. IT IS
IMPORTANT TO REMIND USERS NOT TO FOCUS ON THE EXACT FORECAST
TRACK...ESPECIALLY AT DAYS 4 AND 5...SINCE THE MOST RECENT 5-YEAR
AVERAGE ERRORS AT THOSE FORECAST TIMES ARE 200 AND 250 MILES...
RESPECTIVELY.



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