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#457879 (Received by flhurricane at: 5:00 PM 08.Sep.2011) TCDAT5 TROPICAL STORM NATE DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL152011 400 PM CDT THU SEP 08 2011 ALTHOUGH THE SATELLITE APPEARANCE OF NATE HAS NOT CHANGED MUCH THIS AFTERNOON...AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT HAS REPORTED PEAK 1000-FT FLIGHT-LEVEL WINDS OF 81 KT AND BELIEVABLE SFMR SURFACE WINDS OF AROUND 60 KT. BASED ON THESE DATA...THE INITIAL INTENSITY IS INCREASED TO 60 KT. THE CENTER REMAINS NEAR THE NORTHEASTERN EDGE OF THE DEEP CONVECTION DUE TO LIGHT TO MODERATE NORTHEASTERLY SHEAR. THE SHEAR IS EXPECTED TO WEAKEN DURING THE NEXT 12-24 HOURS...WHICH SHOULD PLACE NATE IN A FAVORABLE ENVIRONMENT FOR STRENGTHENING DURING THE NEXT FEW DAYS. THE UPDATED INTENSITY FORECAST IS ABOVE THE PREVIOUS ADVISORY AND IS A BLEND OF THE SHIPS/LGEM GUIDANCE. FIXES FROM THE AIRCRAFT SHOW THAT NATE HAS MOVED SLOWLY SOUTH-SOUTHEASTWARD DURING THE PAST 24 HOURS. THE INITIAL MOTION ESTIMATE IS 160/2 KT. THE OVERALL FORECAST REASONING HAS CHANGED LITTLE SINCE THIS MORNING. NATE WILL REMAIN IN WEAK STEERING CURRENTS DURING THE NEXT DAY OR SO...THEN IT SHOULD BEGIN MOVING NORTHWARD AROUND THE WESTERN SIDE OF THE CARIBBEAN RIDGE. AFTER 36-48 HOURS...THERE REMAINS A VERY LARGE SPREAD IN THE GUIDANCE... HOWEVER THE MODELS HAVE GENERALLY SHIFTED WESTWARD. THE GFS IS ALONG THE EASTERN EDGE OF THE ENVELOPE AND SHOWS A SLOW NORTHWARD TO NORTH-NORTHWESTWARD MOTION OVER THE CENTRAL GULF OF MEXICO. MOST OF THE REMAINDER OF THE TRACK MODELS MOVE NATE MORE WESTWARD TOWARD MEXICO. THE OFFICIAL FORECAST HAS BEEN SHIFTED TO THE LEFT...BUT NOT NEARLY AS FAR WEST AS THE MULTI-MODEL CONSENSUS...OUT OF RESPECT FOR THE GFS AND THE EARLIER ECMWF ENSEMBLE MEMBERS. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 19.7N 92.3W 60 KT 70 MPH 12H 09/0600Z 19.7N 92.2W 65 KT 75 MPH 24H 09/1800Z 20.2N 92.3W 70 KT 80 MPH 36H 10/0600Z 20.9N 92.8W 75 KT 85 MPH 48H 10/1800Z 21.6N 93.3W 80 KT 90 MPH 72H 11/1800Z 22.5N 94.0W 85 KT 100 MPH 96H 12/1800Z 23.0N 94.5W 85 KT 100 MPH 120H 13/1800Z 23.5N 95.0W 85 KT 100 MPH $$ FORECASTER BROWN |