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#437541 (Received by flhurricane at: 4:37 PM 29.Jun.2011) TCDAT1 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 |