Tropical Storm Sepat moved toward Honshu on Monday. At 11:00 p.m. EDT on Monday the center of Tropical Storm Sepat was located at latitude 29.7°N and longitude 140.7°E which put the center about 420 miles (680 km) south of Tokyo, Japan. Sepat was moving toward the northwest at 14 m.p.h. (22 km/h). The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h). The minimum surface pressure was 1003 mb.
Tropical Storm Sepat strengthened a little on Monday morning, but Sepat was showing signs of weakening on Monday evening. Thunderstorms were still occurring near the center of Tropical Storm Sepat. Thunderstorms were also occurring bands revolving around the center of Sepat’s circulation. Storms near the center of Sepat generated upper level divergence that pumped mass away from the tropical storm. The removal of mass in the upper levels was balanced by the inflow of mass in the lower levels of Tropical Storm Sepat. The balance of upper level divergence and inflow in the lower levels caused the surface pressure to remain steady.
The distribution of wind speeds in Tropical Storm Sepat was asymmetrical. Winds to tropical storm force extended out 110 miles (175 km) in the eastern side of Sepat’s circulation. The winds in the western side of Tropical Storm Sepat were blowing at less than tropical storm force.
Tropical Storm Sepat will move through an environment that will become unfavorable for intensification during the next 24 hours. Sepat will move over water where where the Sea Surface Temperatures are near 26°C. It will move under the northern part of an upper level low south of Japan. The upper level low will produce northeasterly winds that will blow toward the top of Sepat’s circulation. Those winds will cause moderate vertical wind shear. The vertical wind shear and marginal Sea Surface Temperatures will cause Tropical Storm Sepat to weaken during the next 24 hours. Sepat is likely to weaken to a tropical depression on Tuesday.
Tropical Storm Sepat will move around the western end of a high pressure system over the Western North Pacific Ocean. The high pressure system will steer Sepat toward the north-northwest during the next 24 hours. On its anticipated track, Tropical Storm Sepat will continue to move toward Honshu.