Typhoon Koguma continued to weaken on Monday as it moved over the Western North Pacific Ocean east of Japan. At 11:00 p.m. EDT on Monday the center of Typhoon Koguma was located at latitude 34.6°N and longitude 152.6°E which put the center about 690 miles (1110 km) east of Tokyo, Japan. Koguma was moving toward the northeast at 28 m.p.h. (45 km/h). The maximum sustained wind speed was 80 m.p.h. (130 km/h) and there were wind gusts to 100 m.p.h. (160 km/h). The minimum surface pressure was 979 mb.
Typhoon Koguma started to make a transition to a strong extratropical cyclone on Monday. Thunderstorms were still occurring in bands in the eastern and northern parts of Koguma’s circulation. Bands in the western and southern parts of Typhoon Koguma consisted primarily of showers and lower clouds. Storms near the center of Koguma generated upper level divergence that pumped mass away to the northeast of the typhoon. The removal of mass in the upper levels was less than the convergence of mass in the lower levels of the atmosphere. So, the surface pressure increased on Monday.
Even though Typhoon Koguma started a transition to an extratropical cyclone on Monday, the distribution of wind speeds was still fairly symmetrical. Winds to typhoon force extended out 60 miles (95 km) from the center of Koguma’s circulation. Winds to tropical storm force extended out 140 miles (225 km) from the center of Typhoon Koguma.
Typhoon Koguma will move through an environment that will be unfavorable for intensification of a typhoon during the next 24 hours. Koguma will move over water where the Sea Surface Temperatures are near 22°C. It will move under the eastern side of an upper level trough that is east of Japan. The upper level trough will produce southwesterly winds that will blow toward the top of Koguma’s circulation. Those winds will cause strong vertical wind shear. Typhoon Koguma will continue to weaken on Tuesday as it makes a transition to a strong extratropical cyclone.
The upper level trough that is east of Japan will steer Typhoon Koguma quickly toward the northeast during the next 24 hours. On its anticipated track, Typhoon Koguma will move farther away from Japan.