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TROPICAL STORM ARLENE DISCUSSION NUMBER 6

By: National Hurricane Center
By: National Hurricane Center

TROPICAL STORM ARLENE DISCUSSION NUMBER 6
NWS NATIONAL HURRICANE CENTER MIAMI FL AL012011
1000 PM CDT WED JUN 29 2011

AN AIR FORCE HURRICANE HUNTER AIRCRAFT REPORTED PEAK FLIGHT-LEVEL
WINDS OF 64 KT ON ITS FIRST PASS THROUGH ARLENE WHICH EQUATES TO
ABOUT 50 KT SURFACE WINDS AND A MINIMUM PRESSURE OF 996 MB.
SEVERAL SFMR WIND MEASUREMENTS CLOSE TO 50 KT WERE ALSO RECORDED ON
THAT PASS AND THE SUBSEQUENT ONE AROUND 2300 UTC. EARLIER
MICROWAVE PASSES REVEALED A PROMINENT BAND OVER THE SOUTHERN
SEMICIRCLE BUT A LACK OF ANY DISTINGUISHING CENTRAL FEATURES. THE
LATTER MATCHES WHAT THE PLANE ALSO FOUND...A LARGE REGION OF LIGHT
AND VARIABLE WINDS NEAR THE CENTER. ON THE BASIS OF THE PLANE
REPORTS AND 0000 UTC TAFB/SAB SATELLITE CLASSIFICATIONS OF
3.5/3.0...THE INITIAL INTENSITY IS HELD AT 50 KT. ALTHOUGH THE
WINDS ALOFT ARE GENERALLY FAVORABLE AND THE WATERS UNDERNEATH THE
CYCLONE ARE VERY WARM...THE CURRENT STORM STRUCTURE DOES NOT SEEM
SUITABLE FOR SIGNIFICANT INTENSIFICATION. BESIDES...THE WINDOW OF
OPPORTUNITY FOR STRENGTHENING IS DECREASING NOW THAT LANDFALL SEEMS
IMMINENT. THE OFFICIAL NHC FORECAST REMAINS IN LINE WITH THE
STATISTICAL INTENSITY GUIDANCE AND INDICATES ARLENE REACHING A
PEAK INTENSITY NEAR HURRICANE STRENGTH IMMEDIATELY BEFORE LANDFALL.

THE SEQUENCE OF AIRCRAFT FIXES FROM THE MORNING AND LATE AFTERNOON
FLIGHTS YIELDED LITTLE OVERALL MOTION...BUT RECENT SATELLITE IMAGERY
SUGGESTS THAT ARLENE MAY HAVE BEGUN TO MOVE SLIGHTLY FASTER. A
STRONG MID-TROPOSPHERIC AREA OF HIGH PRESSURE BUILDING TO THE NORTH
AND NORTHWEST OF THE CYCLONE SHOULD INDUCE A GENERALLY WESTWARD
TRACK TO NEAR LANDFALL. A TURN TOWARD THE WEST-SOUTHWEST IS
POSSIBLE AFTER THAT AS THE ORIENTATION OF THE RIDGE CHANGES AND AS
THE CYCLONE INTERACTS WITH LAND. THE OFFICIAL NHC FORECAST IS VERY
SIMILAR TO BUT A BIT SLOWER THAN THE PREVIOUS TRACK DUE TO EARLIER
DECELERATION.

AIRCRAFT DATA INDICATE THAT TROPICAL-STORM-FORCE WINDS HAVE EXPANDED
SIGNIFICANTLY TO THE SOUTHWEST AND THE WIND RADII HAVE BEEN
MODIFIED ACCORDINGLY.

FORECAST POSITIONS AND MAX WINDS

INIT 30/0300Z 21.5N 96.1W 50 KT 60 MPH
12H 30/1200Z 21.5N 97.0W 60 KT 70 MPH
24H 01/0000Z 21.3N 98.2W 45 KT 50 MPH...INLAND
36H 01/1200Z 20.7N 99.4W 25 KT 30 MPH...INLAND
48H 02/0000Z 20.5N 100.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 03/0000Z...DISSIPATED

$$
FORECASTER KIMBERLAIN/BROWN


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