Tropical Storm Mun developed near Hainan Island on Tuesday when the Japan Meteorological Agency designated an area of low pressure as a tropical storm. At 5:00 p.m. EDT on Tuesday the center of Tropical Storm Mun was located at latitude 19.4°N and longitude 109.8°E which put the center over Hainan Island and it was about 225 miles (365 km) east-southeast of Hai Phong, Vietnam. Mun was moving toward the west at 12 m.p.h. (19 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 994 mb.
The circulation around Tropical Storm Mun was very large but it did not have a well developed inner core. Winds to tropical storm force extended out several hundred miles from the center of circulation. However, there were few thunderstorms near the center. The strongest thunderstorms were in two bands in the western periphery of the circulation. Other bands around Tropical Storm Mun consisted primarily of showers and lower clouds.
Tropical Storm Mun will move through an environment that is not favorable for intensification. After Mun moves west of Hainan Island the tropical storm will move over water where the Sea Surface Temperature is near 30°C. So, there is plenty of energy in the upper ocean to support intensification. However, Tropical Storm Mun will move south of an upper level ridge over eastern Asia. The ridge will produce strong northeasterly winds which will cause strong vertical wind shear. The wind shear will prevent significant intensification of Tropical Storm Mun.
Since Tropical Storm Mun does not have a well developed inner core with tall thunderstorms, it will be steered by the winds at lower levels in the atmosphere. Southeasterly winds blowing as part of the monsoonal circulation will push Mun toward the border between Vietnam and China. On its anticipated track the center of Tropical Storm Mun will move inland within 24 hours. Mun will bring some gusty winds and locally heavy rain to portions of northeastern Vietnam and southeastern China. Heavy rain could cause flash floods in some locations.