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| #375095 (Received by flhurricane at: 10:59 AM 10.Sep.2010) TCDAT1 TROPICAL STORM IGOR DISCUSSION NUMBER 9 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010 1100 AM AST FRI SEP 10 2010 IGOR REMAINS A SHEARED TROPICAL CYCLONE. DURING THE PAST FEW HOURS...HOWEVER...THE SHEAR HAS BEGUN TO SHOW SIGNS OF ABATING AND THE LOW-LEVEL CENTER IS NOW FARTHER INTO THE EASTERN PORTION OF THE CENTRAL DEEP CONVECTION. THE UPGRADE TO STORM STATUS IS BASED ON A SATELLITE INTENSITY ESTIMATE OF 35 KT FROM TAFB AND A 47-KT UW-CIMSS 3-HR AVERAGE ADT. THE INITIAL MOTION IS 280/14. THE INITIAL POSITION AND MOTION ARE STILL SOMEWHAT UNCERTAIN DUE TO MULTIPLE CIRCULATIONS ROTATING AROUND THE CENTER OF A LARGER CYCLONIC GYRE. HOWEVER...THE MOTION IS EXPECTED TO BE BASICALLY WESTWARD FOR THE NEXT 96 HOURS OR SO ALONG THE SOUTHERN PERIPHERY OF A STRONG SUBTROPICAL RIDGE LOCATED TO THE NORTH OF THE CYCLONE. BY DAY 5...A SERIES OF WEAK SHORTWAVE TROUGHS MOVING THROUGH THE BASE OF A BROAD LONGWAVE TROUGH FORECAST TO BE OFF THE U.S. EAST COAST IS FORECAST BY ALL OF THE GLOBAL MODELS TO CREATE A WEAKNESS IN THE RIDGE BETWEEN 50W-60W LONGITUDE. THIS IS EXPECTED TO WEAKEN THE STEERING FLOW AND CAUSE IGOR TO SLOW DOWN AND ALSO TURN WEST-NORTHWESTWARD. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND THE TVCN MODEL CONSENSUS. CURRENT SHEAR ANALYSES FROM SHIPS AND UW-CIMSS...ALONG WITH WATER VAPOR WINDS...INDICATE THE VERTICAL SHEAR ACROSS IGOR HAS DECREASED FROM 20 KT DOWN TO 10 KT DURING THE PAST 24 HOURS. THIS DECEASING SHEAR TENDENCY IS EXPECTED TO CONTINUE THROUGHOUT THE FORECAST PERIOD AS IGOR MOVES OVER GRADUALLY INCREASING SSTS...ESPECIALLY AFTER 48 HOURS. THE RESULT SHOULD BE STEADY INTENSIFICATION WITH IGOR POSSIBLY REACHING HURRICANE STATUS ON SUNDAY AND MAJOR HURRICANE STATUS BY DAY 5...AS INDICATED BY THE SHIPS...GFDL...AND HWRF MODELS. THE OFFICIAL INTENSITY FORECAST IS A LITTLE BELOW THE GUIDANCE THROUGH 48 HOURS DUE TO UNCERTAINTY ABOUT WHEN IGOR WILL DEVELOP A CONSOLIDATED CENTER OF CIRCULATION...BUT IS CLOSE TO THE GUIDANCE THEREAFTER. FORECAST POSITIONS AND MAX WINDS INITIAL 10/1500Z 16.4N 31.0W 35 KT 12HR VT 11/0000Z 16.6N 33.2W 40 KT 24HR VT 11/1200Z 16.8N 36.2W 45 KT 36HR VT 12/0000Z 17.0N 39.2W 50 KT 48HR VT 12/1200Z 17.1N 41.7W 60 KT 72HR VT 13/1200Z 17.3N 46.2W 70 KT 96HR VT 14/1200Z 18.2N 50.3W 85 KT 120HR VT 15/1200Z 19.5N 53.5W 95 KT $$ FORECASTER STEWART |
