Meteorological history Typhoon Sepat (2007)

map plotting track , intensity of storm, according saffir–simpson scale

on august 11, low-level circulation center formed in conjunction persistent area of convection 1,280 km (800 mi) southeast of naha, okinawa. northerly upper-level winds provided beneficial divergence, though resulted in detrimental wind shear , lack of inflow. upper-level conditions gradually became more favorable development disturbance tracked along eastern periphery of upper-level anticyclone. convective rain bands wrapping circulation, joint typhoon warning center (jtwc) issued tropical cyclone formation alert on system late on august 11. remaining stationary between ridges northeast , southwest, system developed further, , on august 12 jtwc classified tropical depression 09w. shortly thereafter, japan meteorological agency (jma) classified tropical depression while located 1,245 km (774 mi) southeast of okinawa.

twelve hours later, jtwc upgraded tropical depression tropical storm based on dvorak technique satellite intensity estimates , storm exhibiting tightly-curved convective bands. upper-level low helped reduce wind shear had been affecting storm. jtwc warned of possibility of rapid intensification. jma upgraded depression tropical storm later day , named sepat, name contributed malaysia referring freshwater fish species.

by next morning, august 13, sepat had banding eye visible on microwave satellite imagery , had remained in environment conducive strengthening, including weakening wind shear. upper-level anticyclone moved on storm. now, sepat had moved pagasa s area of responsibility , attained local name egay . jma upgraded sepat severe tropical storm shortly after. sepat continued gain more organisation , intensify further, , started move faster under influence of subtropical steering ridge. sepat strengthened typhoon on morning of august 14 under still-decreasing wind shear , favourable diffluence.

sepat developed cloud-filled eye measuring 12 nautical miles (22 km; 14 mi) across later night, part of larger central dense overcast 130 nmi (240 km), 150 mi) wide. favourable sea surface temperatures of 29–30 °c (84–86 °f) allowed sepat continue intensifying despite decrease of poleward outflow. time, sepat had deepened 955 hpa. jtwc noted possible imminent rapid intensification of storm.

late night, sepat underwent rapid intensification expected, , upgraded jtwc super typhoon next morning. jma analysed sepat @ 940 hpa @ same time. deep convection warmed , underwent slight fluctuations during afternoon. during period, sepat slowed in forward speed , took turn west-southwest motion more poleward one. eye cleared out, became larger, , warmed. late night, sepat had become strongest storm of season date, jma analysing pressure @ 925 hpa, lower typhoon man-yi s minimum of 935 hpa.

typhoon sepat during eyewall replacement cycle on august 17

continuing intensify, sepat reached peak minimum central pressure of 910 hpa on morning of august 16. managed maintain cloud-free eye. high ocean heat content , equatorward outflow allowed sepat maintain intensity, eyewall replacement cycle began later night. eyewall replacement cycle continued throughout night, , next morning sepat displayed concentric eyewalls, inner eyewall being weaker. jtwc downgraded typhoon later evening.

it made landfall in eastern taiwan between taitung , hualien on morning of august 18 local time @ around 5 a.m. (2100 utc august 17) , weakened minimal typhoon. after crossing island, sepat held on minimal typhoon intensity before weakening severe tropical storm night. made second landfall, in china, 24 hours after landfall on taiwan , downgraded tropical storm next morning. further weakened inland , jma issued final advisory on morning of august 20.