000 WTNT41 KNHC 290014 TCDAT1 TROPICAL STORM ARLENE SPECIAL DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL012011 700 PM CDT TUE JUN 28 2011 DURING THE PAST FEW HOURS...THERE HAS BEEN AN INCREASE IN THE COVERAGE AND ORGANIZATION OF THE DEEP CONVECTION IN ASSOCIATION WITH THE LOW PRESSURE AREA IN THE SOUTHWESTERN GULF OF MEXICO. DATA T-NUMBERS FROM SPECIAL DVORAK CLASSIFICATIONS AT 2245 UTC FROM SAB AND TAFB WERE 2.5 AND 2.0...RESPECTIVELY. THE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE SYSTEM THIS AFTERNOON ALREADY FOUND AN AREA OF 30 TO 35 KT SURFACE WINDS TO THE NORTHEAST OF THE CENTER. BASED ON THE EARLIER AIRCRAFT OBSERVATIONS AND RECENT SATELLITE TRENDS...THE SYSTEM IS UPGRADED TO A TROPICAL STORM... THE FIRST OF THE 2011 ATLANTIC HURRICANE SEASON. THE INITIAL MOTION ESTIMATE IS 290/6. A MID- TO UPPER-LEVEL WEAKNESS NORTH OF THE TROPICAL CYCLONE IS FORECAST TO LIFT NORTHEASTWARD DURING THE NEXT 24 HOURS AS A RIDGE OVER THE CENTRAL UNTIED STATES BUILDS EASTWARD. THIS SHOULD CAUSE THE TRACK OF ARLENE TO BEND TOWARD THE WEST OR WEST-SOUTHWEST. THE TRACK GUIDANCE IS IN GOOD AGREEMENT ON THIS SCENARIO AND THE NHC FORECAST IS NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE. ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR STRENGTHENING. THE SHEARING AFFECTS OF THE RETREATING UPPER-LEVEL TROUGH ARE LESSENING AND THE SHEAR IS EXPECTED TO DECREASE DURING THE NEXT 24 HOURS. PERHAPS THE ONE LIMITING FACTOR FOR SIGNIFICANT INTENSIFICATION COULD BE THE BROAD NATURE OF THE CYCLONE CIRCULATION. THE OFFICIAL INTENSITY FORECAST IS CLOSE TO THE STATISTICAL MODEL OUTPUT. FORECAST POSITIONS AND MAX WINDS INIT 29/0000Z 21.2N 93.7W 35 KT 40 MPH 12H 29/0600Z 21.7N 94.6W 40 KT 45 MPH 24H 29/1800Z 22.0N 95.9W 45 KT 50 MPH 36H 30/0600Z 22.0N 96.9W 50 KT 60 MPH 48H 30/1800Z 22.0N 97.9W 50 KT 60 MPH 72H 01/1800Z 21.5N 100.0W 25 KT 30 MPH...INLAND 96H 02/1800Z...INLAND $$ FORECASTER BROWN/KIMBERLAIN 000 WTNT41 KNHC 290014 TCDAT1 TROPICAL STORM ARLENE SPECIAL DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL012011 700 PM CDT TUE JUN 28 2011 DURING THE PAST FEW HOURS...THERE HAS BEEN AN INCREASE IN THE COVERAGE AND ORGANIZATION OF THE DEEP CONVECTION IN ASSOCIATION WITH THE LOW PRESSURE AREA IN THE SOUTHWESTERN GULF OF MEXICO. DATA T-NUMBERS FROM SPECIAL DVORAK CLASSIFICATIONS AT 2245 UTC FROM SAB AND TAFB WERE 2.5 AND 2.0...RESPECTIVELY. THE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE SYSTEM THIS AFTERNOON ALREADY FOUND AN AREA OF 30 TO 35 KT SURFACE WINDS TO THE NORTHEAST OF THE CENTER. BASED ON THE EARLIER AIRCRAFT OBSERVATIONS AND RECENT SATELLITE TRENDS...THE SYSTEM IS UPGRADED TO A TROPICAL STORM... THE FIRST OF THE 2011 ATLANTIC HURRICANE SEASON. THE INITIAL MOTION ESTIMATE IS 290/6. A MID- TO UPPER-LEVEL WEAKNESS NORTH OF THE TROPICAL CYCLONE IS FORECAST TO LIFT NORTHEASTWARD DURING THE NEXT 24 HOURS AS A RIDGE OVER THE CENTRAL UNTIED STATES BUILDS EASTWARD. THIS SHOULD CAUSE THE TRACK OF ARLENE TO BEND TOWARD THE WEST OR WEST-SOUTHWEST. THE TRACK GUIDANCE IS IN GOOD AGREEMENT ON THIS SCENARIO AND THE NHC FORECAST IS NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE. ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR STRENGTHENING. THE SHEARING AFFECTS OF THE RETREATING UPPER-LEVEL TROUGH ARE LESSENING AND THE SHEAR IS EXPECTED TO DECREASE DURING THE NEXT 24 HOURS. PERHAPS THE ONE LIMITING FACTOR FOR SIGNIFICANT INTENSIFICATION COULD BE THE BROAD NATURE OF THE CYCLONE CIRCULATION. THE OFFICIAL INTENSITY FORECAST IS CLOSE TO THE STATISTICAL MODEL OUTPUT. FORECAST POSITIONS AND MAX WINDS INIT 29/0000Z 21.2N 93.7W 35 KT 40 MPH 12H 29/0600Z 21.7N 94.6W 40 KT 45 MPH 24H 29/1800Z 22.0N 95.9W 45 KT 50 MPH 36H 30/0600Z 22.0N 96.9W 50 KT 60 MPH 48H 30/1800Z 22.0N 97.9W 50 KT 60 MPH 72H 01/1800Z 21.5N 100.0W 25 KT 30 MPH...INLAND 96H 02/1800Z...INLAND $$ FORECASTER BROWN/KIMBERLAIN