TROPICAL STORM ARLENE DISCUSSION NUMBER 5

By: National Hurricane Center
By: National Hurricane Center

TROPICAL STORM ARLENE DISCUSSION NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL012011
400 PM CDT WED JUN 29 2011

THERE HAS NOT BEEN MUCH CHANGE IN THE ORGANIZATION OF THE CLOUD
PATTERN SINCE THIS MORNING. MOST OF THE DEEP CONVECTION WAS
OCCURRING OVER THE SOUTHERN PORTION OF THE CIRCULATION...ALTHOUGH
RECENTLY THERE HAVE BEEN INDICATIONS OF CONVECTIVE BANDS BEGINNING
TO WRAP AROUND THE NORTHEASTERN QUADRANT OF THE STORM. THE
INTENSITY IS HELD AT 45 KT FOR THIS ADVISORY...WITH ANOTHER
HURRICANE HUNTER MISSION SCHEDULED TO PENETRATE THE CENTER VERY
SOON. THE SHIPS RAPID INTENSIFICATION INDEX CONTINUES TO SHOW A
SIGNIFICANT PROBABILITY OF A 25 TO 30 KT INCREASE OVER 24
HOURS...HOWEVER INTERACTION WITH LAND WOULD HALT STRENGTHENING
SOONER THAN THAT TIME FRAME. THE LACK OF A WELL-DEFINED INNER CORE
MITIGATES THE INCREASINGLY CONDUCIVE ATMOSPHERIC ENVIRONMENT FOR
STRENGTHENING. IT IS POSSIBLE FOR ARLENE TO REACH A PEAK INTENSITY
OF 55-65 KT BETWEEN THE 12 HR FORECAST POINT AND LANDFALL...AND
THUS THE SYSTEM STILL HAS THE POTENTIAL TO BECOME A HURRICANE.

THE ABOVE-MENTIONED SOUTHERN CONVECTIVE ASYMMETRY MAY HAVE PARTIALLY
EXPLAINED THE SOUTHWARD COMPONENT OF MOTION NOTED IN THE AIRCRAFT
FIXES FROM EARLIER TODAY. A LONGER-TERM...AND LIKELY MORE
REPRESENTATIVE...MOTION ESTIMATE IS NOW ABOUT 270/6. A STRONG
MID-TROPOSPHERIC HIGH PRESSURE AREA TO THE NORTH AND NORTHWEST OF
ARLENE SHOULD CAUSE A MOSTLY WESTWARD TRACK FOR THE NEXT DAY OR SO
WITH A TURN TO THE WEST-SOUTHWEST THEREAFTER. THE LATTER HAS OFTEN
BEEN NOTED AS TROPICAL CYCLONES INTERACT WITH THE VERY HIGH TERRAIN
OF THE SIERRA MADRE ORIENTAL MOUNTAINS OF MEXICO. MOST OF THE
TRACK GUIDANCE MODELS ARE IN AGREEMENT ON THIS GENERAL SCENARIO AS
WELL.

GIVEN THE LARGE SIZE OF THE CIRCULATION OF ARLENE...ONE SHOULD NOT
FOCUS ON THE EXACT FORECAST TRACK...AS IMPACTS WILL LIKELY BE FELT
OVER A LARGE PORTION OF NORTHEASTERN MEXICO WELL AWAY FROM THE
CENTER.

FORECAST POSITIONS AND MAX WINDS

INIT 29/2100Z 21.1N 96.1W 45 KT 50 MPH
12H 30/0600Z 21.1N 96.9W 55 KT 65 MPH
24H 30/1800Z 21.0N 98.0W 50 KT 60 MPH...INLAND
36H 01/0600Z 20.6N 99.5W 25 KT 30 MPH...INLAND
48H 01/1800Z 20.0N 101.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
72H 02/1800Z...DISSIPATED

$$
FORECASTER PASCH


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