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#445548 (Received by flhurricane at: 4:40 AM 29.Jul.2011) TCDAT4 TROPICAL STORM DON DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042011 400 AM CDT FRI JUL 29 2011 DON CONTINUES TO HAVE A SHEARED APPEARANCE ON SATELLITE IMAGES WITH THE LOW-LEVEL CENTER DISPLACED NEAR THE NORTHERN EDGE OF AN ELONGATED AREA OF STRONG CONVECTION. THIS SHEAR CAN ALSO BE SEEN IN RECONNAISSANCE DATA...WHICH SHOWED THAT THE SURFACE CENTER IS DISPLACED SOMEWHAT TO THE NORTH OF THE 850 MB FLIGHT-LEVEL CENTER. THE INITIAL INTENSITY REMAINS 45 KT...A BLEND OF THE ESTIMATES FROM SATELLITE AND AIRCRAFT DATA. MODERATE NORTHERLY SHEAR IS FORECAST UNTIL DON MAKES LANDFALL ALONG WITH SOME DRY AIR ALOFT. THIS COMBINATION WILL PROBABLY LIMIT SIGNIFICANT INTENSIFICATION EVEN THOUGH THE STORM IS MOVING OVER VERY WARM WATERS. MOST OF THE GUIDANCE SHOWS JUST A LITTLE MORE STRENGTHENING...AND THE OFFICIAL INTENSITY FORECAST IS BASICALLY AN UPDATE OF THE PREVIOUS PACKAGE. AFTER MOVING THROUGH TEXAS...THIS SMALL SYSTEM WILL NOT LAST VERY LONG AFTER INTERACTING WITH THE HIGH TERRAIN OF MEXICO...AND DISSIPATION IS LIKELY BETWEEN 36 AND 48 HOURS. AIRCRAFT FIXES SUGGEST DON IS MOVING ABOUT 295/12. HIGH PRESSURE RIDGING OVER THE SOUTHERN UNITED STATES WILL PROBABLY STEER THE CYCLONE ALONG THAT GENERAL COURSE UNTIL LANDFALL...PERHAPS EVEN A LITTLE MORE TO THE LEFT AS THE RIDGE BUILDS. THE GUIDANCE IS IN GOOD AGREEMENT...ALTHOUGH THE USUALLY RELIABLE ECMWF MODEL IS FARTHER TO THE NORTHEAST. AN EXAMINATION OF THE ECMWF FIELDS INDICATES THAT THE MODEL DECOUPLES THE LOW- AND MID-LEVEL CENTERS...ALLOWING DON TO MOVE MORE TO THE NORTHWEST. THIS DOES NOT SEEM LIKELY AS ENVIRONMENTAL CONDITIONS ARE NOT EXPECTED TO CHANGE SIGNIFICANTLY FROM NOW UNTIL LANDFALL. THUS THE NHC FORECAST WILL STAY CLOSE TO THE DYNAMICAL MODEL CONSENSUS AND THE PREVIOUS FORECAST. INTERESTS IN EXTREME NORTHEAST MEXICO SHOULD CLOSELY MONITOR THE PROGRESS OF DON. AN UNEXPECTED SMALL DEVIATION TO THE SOUTH OF THE FORECAST TRACK COULD NECESSITATE THE ISSUANCE OF WARNINGS FOR THE EXTREME NORTHEASTERN COAST OF MEXICO. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 25.3N 93.6W 45 KT 50 MPH 12H 29/1800Z 26.1N 95.5W 50 KT 60 MPH 24H 30/0600Z 27.0N 97.8W 45 KT 50 MPH...INLAND 36H 30/1800Z 27.8N 100.4W 30 KT 35 MPH...INLAND 48H 31/0600Z...DISSIPATED $$ FORECASTER BLAKE/STEWART |