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| #457706 (Received by flhurricane at: 4:48 AM 08.Sep.2011) TCDAT5 TROPICAL STORM NATE DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL152011 400 AM CDT THU SEP 08 2011 NATE APPEARS TO BE SLOWLY BECOMING BETTER ORGANIZED. A CURVED BAND NOW WRAPS AROUND THE NORTHWEST SEMICIRCLE. HOWEVER...CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY THAT THE MAIN CONVECTIVE MASS IS CONFINED TO THE SOUTHWEST QUADRANT...WITH THE LOW-LEVEL CENTER STILL DISPLACED ABOUT 60 N MI NORTHEAST OF IT. DVORAK T-NUMBERS FROM TAFB AND SAB HAVE INCREASED SOME SINCE 0000 UTC BUT REMAIN BELOW TROPICAL STORM STRENGTH. A SHIP LOCATED ABOUT 50 N MI SOUTHEAST OF THE CENTER REPORTED 45 KT WIND AT 0300 UTC...BUT THIS OBSERVATION WAS JUDGED TO BE A BIT HIGH. BASED UPON THESE DATA...THE INITIAL INTENSITY ESTIMATE IS HELD AT 40 KT. THE CENTER OF NATE APPEARS TO HAVE NOT MOVED MUCH RECENTLY. HOWEVER...SINCE THE CENTER REMAINS HARD TO LOCATE...THE INITIAL MOTION ESTIMATE OF 090/02 REMAINS AS UNCERTAIN AS IT WAS EARLIER. THE CYCLONE REMAINS IN A WEAK STEERING FLOW IN BETWEEN MID-LEVEL RIDGES OVER THE NORTHERN CARIBBEAN AND MEXICO...WITH SHOULD ONLY ALLOW A SLOW AND ERRATIC MOTION FOR THE NEXT DAY OR SO. AFTER THAT...A SLOW NORTHWESTWARD TO NORTHWESTWARD MOTION SHOULD COMMENCE UNTIL ABOUT 72 HOURS AS THE MID-LEVEL RIDGE TO THE EAST OF NATE LIFTS NORTHWARD. LATER IN THE FORECAST PERIOD...GLOBAL MODELS SHOW THE MEXICAN RIDGE BUILDING EASTWARD AND INDUCING A GENERALLY WESTWARD TRACK. WHILE THERE CONTINUES TO BE A FAIR AMOUNT OF NORTH-TO-SOUTH SPREAD IN THE TRACK GUIDANCE THIS CYCLE....THE MORE RELIABLE GFS/ECWMF REMAIN THE MOST CONSISTENT. ONLY MINOR CHANGES WERE MADE TO THE PREVIOUS TRACK FORECAST...WITH THE NEW TRACK IN BEST AGREEMENT WITH THE GFS/ECMWF SOLUTIONS. THE INTENSITY FORECAST FOR NATE IS CHALLENGING. WHILE THE CYCLONE IS LOCATED IN A DIFFLUENT UPPER-LEVEL WIND ENVIRONMENT...WATER VAPOR IMAGERY SHOWS A TONGUE OF EXCEPTIONALLY DRY AIR NEAR AND NORTH OF NATE. THIS...AND THE RELATIVE LACK OF CONVECTIVE ORGANIZATION... WOULD ARGUE AGAINST ANY SIGNIFICANT INTENSIFICATION IN THE SHORT TERM. LATER IN THE FORECAST PERIOD...SHIPS GUIDANCE STILL INDICATES THE PRESENCE OF A RELATIVELY DRY LOW- TO MID-LEVEL AIR MASS AND A SUDDEN INCREASE IN SOUTHWESTERLY SHEAR ASSOCIATED WITH A TROUGH OVER THE SOUTHEASTERN UNITED STATES. THIS SUGGESTS THAT THE STRONGER DYNAMICAL GUIDANCE...E.G. HWRF...MAY BE IN DOUBT. THE OFFICIAL NHC OFFICIAL IS SIMILAR TO THE PREVIOUS ONE AND PUTS MORE WEIGHT ON THE STATISTICAL INTENSITY MODEL OUTPUT. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 20.4N 92.4W 40 KT 45 MPH 12H 08/1800Z 20.4N 92.2W 45 KT 50 MPH 24H 09/0600Z 20.6N 92.2W 50 KT 60 MPH 36H 09/1800Z 21.2N 92.5W 55 KT 65 MPH 48H 10/0600Z 21.8N 93.0W 60 KT 70 MPH 72H 11/0600Z 22.7N 94.2W 65 KT 75 MPH 96H 12/0600Z 23.0N 95.5W 70 KT 80 MPH 120H 13/0600Z 23.0N 97.0W 70 KT 80 MPH $$ FORECASTER KIMBERLAIN/PASCH |
