Tropical Storm Mun formed over the Western North Pacific Ocean southeast of Japan on Wednesday.  At 5:00 p.m. EDT on Wednesday the center of Tropical Storm Mun was located at latitude 27.1°N and longitude 145.5°E which put the center about 680 miles (1100 km) south-southeast of Tokyo, Japan.  Mun was moving toward the northwest at 10 m.p.h. (16 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 1000 mb.

A low pressure system over the Western North Pacific Ocean southeast of Japan strengthened on Wednesday and the Japan Meteorological Agency designated the system as Tropical Storm Mun.

Tropical Storm Mun was under the eastern side of an upper level low southeast of Japan.  The upper level low was producing southwesterly winds that were blowing across the eastern part of Mun’s circulation.  Those winds were causing moderate vertical wind shear.  The vertical wind shear was causing the distribution of thunderstorms in Tropical Storm Mun to be asymmetrical.  Thunderstorms were occurring in bands in the western side of Mun’s circulation.  Bands in the eastern side of Tropical Storm Mun consisted primarily of showers and lower clouds.  Storms near the center of Mun generated upper level divergence that pumped mass away to the northeast of the tropical storm.

The vertical wind shear was also affecting the distribution of wind speeds in Tropical Storm Mun.  Winds to tropical storm force extended out 85 miles (135 km) in the northern side of Mun’s circulation.  Winds to tropical storm force extended out 40 miles (65 km) in the southern part of Tropical Storm Mun.

Tropical Storm Mun will move through an environment that will be somewhat favorable for intensification during the next 24 hours.  Mun will move over water where where the Sea Surface Temperatures are near 28°C.  However, the upper level low southeast of Japan will continue to cause moderate vertical wind shear.  The vertical wind shear will inhibit intensification.  Tropical Storm Mun could intensify during the next 24 hours if the vertical wind shear does not increase.

The upper level low southeast of Japan will steer Tropical Storm Mun toward the north-northwest during the next 24 hours.  On its anticipated track, Tropical Storm Mun will move toward eastern Japan.  Mun could meander east of Japan during the next few days.