000 WTNT42 KNHC 161457 TCDAT2 HURRICANE JULIA DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122010 1100 AM AST THU SEP 16 2010 SATELLITE IMAGERY CONTINUES TO INDICATE WARMING OF THE CLOUD TOPS IN THE RATHER RAGGED LOOKING CENTRAL DENSE OVERCAST. A 1001Z AMSU MICROWAVE OVERPASS INDICATED A 25-30 NMI DIAMETER EYE THAT WAS OPEN IN THE SOUTHEAST QUADRANT. WATER VAPOR IMAGERY ALSO SHOWS A LARGE SLUG OF DRY AIR BEING ENTRAINED INTO THE EASTERN SEMICIRCLE...WHICH LIKELY EXPLAINS THE EROSION OF THE EASTERN EYEWALL NOTED IN THE AMSU IMAGERY. DESPITE THE AFOREMENTIONED NEGATIVE FACTORS...JULIA HAS MAINTAINED GOOD OUTFLOW TO THE WEST AND NORTH OF THE CYCLONE. THE INITIAL MOTION ESTIMATE HAS INCREASED SHARPLY TO 300/22. JULIA IS EXPECTED TO MOVE TO THE WEST-NORTHWEST AND THEN NORTHWEST FOR THE NEXT 36-48 HOURS AS THE HURRICANE ROUNDS THE SOUTHERN PERIPHERY OF A LARGE SUBTROPICAL RIDGE SITUATED TO ITS NORTH AND NORTHEAST. AFTER THAT...SIGNIFICANT VERTICAL WIND SHEAR MAY WEAKEN THE CYCLONE AND CAUSE IT TO BECOME MORE SHALLOW...AND THEN BE STEERED MORE NORTHWARD SIMILAR TO THE ECMWF AND GFDL MODELS...BUT NOT AS FAR NORTH AND WEST AS THE SHALLOW BAM MODEL. THE OFFICIAL TRACK FORECAST HAS BEEN NUDGED TO THE LEFT OF THE PREVIOUS ADVISORY THROUGH 72 HOURS...AND IS SIMILAR TO THE MULTI-MODEL CONSENSUS. DRY AIR AND COOLER SSTS SHOULD CONTINUE THE RECENT WEAKENING TREND...ESPECIALLY AFTER 24 HOURS. BY 36-48 HOURS...ALL OF THE GLOBAL MODELS INDICATE THAT JULIA WILL BE MOVING INTO A REGION OF STRONG UPPER-LEVEL SHEAR CAUSED BY THE PRONOUNCED NORTHERLY OUTFLOW EMANATING FROM THE MAJOR HURRICANE IGOR LOCATED TO ITS WEST. WITH JULIA MOVING INTO 50-70 KT OF 200 MB WINDS...IT WILL BE HARD FOR JULIA TO SURVIVE AS A TROPICAL CYCLONE AS INDICATED BY THE GLOBAL MODELS AND GFDL/HWRF MODELS. THE OFFICIAL INTENSITY FORECAST SHOWS A FASTER WEAKENING TREND THAN THE PREVIOUS ADVISORY...BUT NOT AS FAST AS THE SHIPS MODEL...WHICH DISSIPATES JULIA BY 120 HOURS. FORECAST POSITIONS AND MAX WINDS INITIAL 16/1500Z 22.4N 38.6W 85 KT 12HR VT 17/0000Z 23.7N 41.2W 75 KT 24HR VT 17/1200Z 25.5N 44.6W 65 KT 36HR VT 18/0000Z 27.3N 47.3W 55 KT 48HR VT 18/1200Z 29.3N 49.1W 45 KT 72HR VT 19/1200Z 33.2N 49.6W 35 KT 96HR VT 20/1200Z 35.8N 46.3W 35 KT 120HR VT 21/1200Z 38.0N 42.0W 35 KT $$ FORECASTER STEWART