000 WTNT45 KNHC 081458 TCDAT5 TROPICAL STORM NATE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL152011 1000 AM CDT THU SEP 08 2011 EARLY MORNING VISIBLE SATELLITE IMAGES SHOW A MORE ORGANIZED TROPICAL CYCLONE THAN WAS SEEN LATE YESTERDAY AFTERNOON. NATE HAS THE APPEARANCE OF A SHEARED TROPICAL CYCLONE WITH THE CENTER LOCATED NEAR THE NORTHEASTERN TIP OF THE MAIN CONVECTIVE MASS. THE INITIAL WIND SPEED IS RAISED TO 45 KT...BASED ON A SHIP OBSERVATION OF 40 KT TO THE SOUTHEAST OF THE CENTER...AND RECENT STRONGER WIND REPORTS FROM ELEVATED PEMEX OIL RIGS IN THE BAY OF CAMPECHE. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO INVESTIGATE NATE THIS AFTERNOON AND SHOULD PROVIDE A BETTER ASSESSMENT OF THE INTENSITY. NATE HAS NOT MOVED MUCH OVERNIGHT OR THIS MORNING...ALTHOUGH THE LATEST SATELLITE AND MICROWAVE IMAGERY SUGGESTS THAT THE CENTER IS A LITTLE SOUTH OF THE EARLIER ESTIMATES. THE CYCLONE IS FORECAST TO REMAIN IN A WEAK STEERING PATTERN BETWEEN MID-LEVEL RIDGES OVER MEXICO AND THE NORTHERN CARIBBEAN DURING THE NEXT 12-24 HOURS. IN A DAY OR SO...NATE IS EXPECTED TO MOVE SLOWLY NORTHWARD AROUND THE WESTERN PERIPHERY OF THE CARIBBEAN RIDGE. AFTER 36-48 HOURS...THE MODEL SPREAD BECOMES INCREASINGLY LARGE...AS SUBTLE DIFFERENCES IN THE STRENGTH AND ORIENTATION OF A MID/UPPER-LEVEL LOW AND TROUGH EXTENDING FROM THE OHIO VALLEY SOUTHWESTWARD HAVE SIGNIFICANT IMPLICATIONS ON THE FUTURE TRACK OF THE CYCLONE. THE LATEST GFS AND GFDL MODELS...WHICH SHOW A SLIGHTLY DEEPER TROUGH...MOVE NATE NORTHWARD TOWARD THE NORTHERN GULF COAST. THE ECMWF AND NOGAPS MODELS DEPICT A WEAKER TROUGH THAT DOES NOT CAPTURE NATE AND ALLOWS IT TURN TURN WESTWARD TOWARD MEXICO TO THE SOUTH OF A BUILDING RIDGE...ALTHOUGH IT SHOULD BE NOTED THAT THERE IS CONSIDERABLE SPREAD AMONG THE ECMWF ENSEMBLE MEMBERS. THE OFFICIAL FORECAST HAS BEEN SHIFTED TO THE RIGHT AND LIES BETWEEN THESE TWO VIABLE SCENARIOS BUT HAS NOT BEEN SHIFTED AS FAR AS THE TVCA CONSENSUS. THE NOAA G-IV AIRCRAFT IS SCHEDULED TO PERFORM A SYNOPTIC SURVEILLANCE MISSION LATER TODAY...WHICH WILL HOPEFULLY HELP REDUCE THE SPREAD IN THE TRACK GUIDANCE TONIGHT. NATE IS CURRENTLY LOCATED IN AN ENVIRONMENT OF LIGHT TO MODERATE NORTHEASTERLY SHEAR. THE SHEAR IS FORECAST TO LESSEN DURING THE NEXT DAY OR SO...WHICH SHOULD ALLOW FOR GRADUAL STRENGTHENING. LATER IN THE FORECAST PERIOD...SOUTHWESTERLY SHEAR IS EXPECTED TO INCREASE AND ALONG WITH DRIER LOW- TO MID-LEVEL AIR...IS FORECAST TO SLOW THE INTENSIFICATION PROCESS. THE UPDATED INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND IS IN GOOD AGREEMENT WITH THE SHIPS/LGEM GUIDANCE. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 20.0N 92.4W 45 KT 50 MPH 12H 09/0000Z 20.4N 92.2W 55 KT 65 MPH 24H 09/1200Z 21.0N 92.2W 55 KT 65 MPH 36H 10/0000Z 21.8N 92.7W 60 KT 70 MPH 48H 10/1200Z 22.5N 93.2W 65 KT 75 MPH 72H 11/1200Z 23.1N 93.8W 70 KT 80 MPH 96H 12/1200Z 23.6N 94.4W 70 KT 80 MPH 120H 13/1200Z 24.0N 95.0W 70 KT 80 MPH $$ FORECASTER BROWN