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| #375729 (Received by flhurricane at: 4:41 AM 13.Sep.2010) TCDAT2 TROPICAL STORM JULIA DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122010 500 AM AST MON SEP 13 2010 THERE HAS NOT BEEN MUCH CHANGE TO THE OVERALL ORGANIZATION OF THE CLOUD PATTERN OF JULIA. MOST OF THE BANDING FEATURES ARE OVER THE WESTERN SEMICIRCLE OF THE CIRCULATION WITH PERHAPS A SLIGHT INCREASE IN DEEP CONVECTION NEAR THE CENTER. DVORAK INTENSITY ESTIMATES FROM BOTH SAB AND TAFB ARE 35 KT...SO THE WIND SPEED IS UNCHANGED FROM THE PREVIOUS ADVISORY. VERTICAL SHEAR IS EXPECTED TO BE WEAK FOR THE NEXT DAY OR TWO AS JULIA MOVES AWAY FROM AN AREA OF STRONG UPPER-LEVEL EASTERLIES ASSOCIATED WITH A RIDGE OVER WEST AFRICA. LATER IN THE FORECAST PERIOD THE TROPICAL CYCLONE COULD EXPERIENCE A SIGNIFICANT INCREASE IN SHEAR DUE TO THE INFLUENCE OF AN UPPER-LEVEL TROUGH OVER THE EASTERN SUBTROPICAL ATLANTIC...WHICH WOULD LIMIT INTENSIFICATION. THERE IS THE POSSIBILITY THAT A CYCLONE WILL CUT OFF FROM THE TROUGH AND BECOME SITUATED TO THE SOUTH OR SOUTHWEST OF JULIA. THIS SCENARIO COULD RESULT IN LESS SHEAR AND ALLOW MORE STRENGTHENING NEAR THE END OF THE PERIOD. HOWEVER...THE GFS INPUT TO THE SHIPS AND LGEM MODELS SHOWS 25 TO 35 KT OF SHEAR AT 96-120 HOURS. GIVEN THE UNCERTAINTIES THE OFFICIAL FORECAST...LIKE THE PREVIOUS ONE...SHOWS NO CHANGE IN STRENGTH BEYOND 48 HOURS. THIS IS CLOSE TO THE INTENSITY MODEL CONSENSUS THROUGH 48 HOURS AND IS SIMILAR TO THE LGEM GUIDANCE FOR DAYS 3 TO 5. LATEST CENTER FIXES ARE A BIT TO THE NORTH OF THE PREVIOUS TRACK. THIS MAY BE THE RESULT OF SOME REFORMATION OR MERELY BECAUSE THE CENTER HAS BEEN DIFFICULT TO LOCATE. AFTER SOME ADJUSTMENTS...THE INITIAL MOTION IS ESTIMATED TO BE 300/11. NOTWITHSTANDING THE SLIGHT NORTHWARD ADJUSTMENT...THE TRACK FORECAST REASONING REMAINS ESSENTIALLY THE SAME AS IN THE PREVIOUS ADVISORY. JULIA IS EXPECTED TO MOVE WEST-NORTHWESTWARD AROUND THE SOUTHWESTERN SIDE OF A MID-LEVEL RIDGE THAT EXTENDS FROM AFRICA WESTWARD INTO THE EASTERN ATLANTIC. IN ABOUT 48 HOURS...A WEAKNESS IN THE RIDGE SHOULD CAUSE THE TROPICAL CYCLONE TO TURN NORTHWESTWARD. THERE IS A FAIR AMOUNT OF SPREAD IN THE MODEL FORECAST TRACKS FOR DAYS 3 TO 5....AND THE OFFICIAL FORECAST IS BASICALLY DOWN THE MIDDLE OF THE SUITE. THIS IS CLOSE TO BUT A TAD SLOWER THAN THE MODEL CONSENSUS DURING THE LATTER HALF OF THE FORECAST PERIOD...AND ALSO A LITTLE NORTH OF THE PREVIOUS NHC FORECAST TRACK DUE TO THE NORTHWARD RELOCATION. FORECAST POSITIONS AND MAX WINDS INITIAL 13/0900Z 14.4N 24.6W 35 KT 12HR VT 13/1800Z 15.1N 26.2W 45 KT 24HR VT 14/0600Z 16.2N 28.2W 50 KT 36HR VT 14/1800Z 17.5N 30.1W 55 KT 48HR VT 15/0600Z 19.0N 31.9W 65 KT 72HR VT 16/0600Z 22.5N 36.0W 65 KT 96HR VT 17/0600Z 25.5N 41.0W 65 KT 120HR VT 18/0600Z 28.5N 46.5W 65 KT $$ FORECASTER PASCH |
