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HURRICANE IRENE DISCUSSION NUMBER 13

Published on August 23, 2011 2:04 PM | Comments

HURRICANE IRENE DISCUSSION NUMBER 13
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
1100 AM EDT TUE AUG 23 2011

THE LAST FEW VISIBLE SATELLITE IMAGES SHOW A HINT OF AN EYE... WHILE
RECENT MICROWAVE DATA SHOW AN EYEWALL THAT IS OPEN TO THE SOUTH.
THE LATEST SATELLITE INTENSITY ESTIMATES FROM SAB AND TAFB WERE 77
AND 90 KT...RESPECTIVELY...AND SUPPORT MAINTAINING AN INITIAL
INTENSITY OF 85 KT. THE RECONNAISSANCE AIRCRAFT SCHEDULED TO
INVESTIGATE IRENE THIS MORNING HAD ISSUES WITH THE ON-BOARD RADAR.
THIS REQUIRED A CHANGE IN AIRCRAFT AND THE NEW PLANE JUST PASSED
THROUGH THE CENTER...REPORTING A MINIMUM PRESSURE OF 980 MB...ABOUT
THE SAME AS DURING THE PREVIOUS MISSION.

A SHEAR ANALYSIS FROM UW-CIMSS SHOWS ABOUT 10-20 KT OF SOUTHWESTERLY
SHEAR OVER IRENE....AND THE SHIPS GUIDANCE DOES NOT WEAKEN THIS
SHEAR DURING THE NEXT COUPLE OF DAYS. AS A RESULT...THE SHIPS/LGEM
MODELS DO NOT SHOW MUCH STRENGTHENING DURING THAT TIME. ON THE
OTHER HAND...THE GFDL/HWRF MODELS ARE MUCH MORE AGGRESSIVE AND MAKE
IRENE A MAJOR HURRICANE WITHIN 24 HOURS. THE NEW INTENSITY FORECAST
IS HIGHER THAN THE STATISTICAL GUIDANCE...BUT NOT AS AGGRESSIVE AS
THE GFDL/HWRF. THE UPDATED FORECAST IS SLIGHTLY BELOW THE PREVIOUS
ADVISORY.

IRENE HAS BEEN MOVING WEST-NORTHWESTWARD OR 295 DEGREES AT 10 KT. A
MID/UPPER-LEVEL TROUGH MOVING OVER THE NORTHEASTERN UNITED STATES
IS EXPECTED TO WEAKEN THE WESTERN PORTION OF THE SUBTROPICAL RIDGE
DURING THE NEXT DAY OR SO. THIS SHOULD ALLOW IRENE TO TURN
NORTHWESTWARD WITHIN THE NEXT 24-36 HOURS...AND THE TRACK GUIDANCE
IS IN EXCELLENT AGREEMENT DURING THE FIRST 48 HOURS. LATER IN THE
FORECAST PERIOD IRENE IS FORECAST TO TURN NORTHWARD AS IT ROUNDS
THE WESTERN PORTION OF THE RIDGE. THE SPREAD IN THE GUIDANCE
INCREASES BY DAY THREE...RANGING FROM THE COASTAL MID-ATLANTIC
STATES TO WELL OFFSHORE...WITH THE UKMET ALONG THE LEFT SIDE AND
THE GFS/NOGAPS ALONG THE RIGHT SIDE OF THE GUIDANCE ENVELOPE. THE
UPDATED TRACK IS CLOSEST TO THE ECMWF AND IS A LITTLE LEFT OF THE
MULTI-MODEL CONSENSUS. 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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