Tropical Storm Yun-yeung formed over the Western North Pacific Ocean south of Japan on Tuesday night. At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Yun-yeung was located at latitude 26.2°N and longitude 133.6°E which put it about 810 miles (1305 km) south-southwest of Tokyo, Japan. Yun-yeung was moving toward the north at 17 m.p.h. (28 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 998 mb.

A low pressure system over the Western North Pacific Ocean strengthened on Tuesday and the Japan Meteorological Agency designated the system as Tropical Storm Yun-yeung. More thunderstorms developed near the center of Yun-yeung’s circulation on Tuesday evening, but the distribution of thunderstorms was asymmetrical. Most of the thunderstorms were occurring in bands in the southern half of Tropical Storm Yun-yeung. Bands in the northern half of the circulation consisted primarily of showers and lower clouds. The distribution of wind speeds was also asymmetrical. Winds to tropical storm force extended out 40 miles (65 km) in the eastern side of Yun-yeung’s circulation. The winds in the eastern side of Yun-yeung were blowing at less than tropical storm force.

Tropical Storm Yun-yeung will move through an environment somewhat favorable for intensification during the next 24 hours. Yun-yeung will move over water where the Sea Surface Temperatures are near 28°C. It will move under the eastern side on an upper level ridge south of Japan. The upper level ridge will produce northeasterly winds that will blow toward the top of Yun-yeung’s circulation. Those winds will cause moderate vertical wind shear. The wind shear is already contributing to the asymmetrical distribution of thunderstorms. The vertical wind shear will inhibit intensification, but the shear will probably not be strong enough to prevent Yun-yeung from strengthening. Tropical Storm Yun-yeung is likely to intensify gradually during the next 24 hours.

Tropical Storm Yun-yeung will move around the northwestern part of high pressure system over the Western North Pacific. The high pressure system will steer Yun-yeung toward the north-northeast during the next 24 hours. On its anticipated track, Tropical Storm Yun-yeung will move closer to Honshu. Yun-yeung could be near Tokyo in 48 hours.