000 WTNT41 KNHC 300240 TCDAT1 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 000 WTNT41 KNHC 300240 TCDAT1 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