Tropical Storm Bolaven formed over the South China Sea near the Spratly Islands on Tuesday. At 10:00 p.m. EDT on Tuesday the center of Tropical Storm Bolaven was located at latitude 10.4°N and longitude 115.1°E which put it about 620 miles (1000 km) east of Ho Chi Minh City, Vietnam. Bolaven was moving toward the west-northwest at 21 m.p.h. (33 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 1002 mb.
A low level center of circulation developed on the eastern side of a cluster of thunderstorms that moved across the southern Philippines on Monday. The center exhibited greater organization on Tuesday and the Japan Meteorological Agency designated the system as Tropical Storm Bolaven. The structure of Tropical Storm Bolaven is asymmetrical. The strongest thunderstorms are occurring northwest of the center of circulation. Thin bands of low clouds and showers were revolving around the center of circulation in the other quadrants of Tropical Storm Bolaven.
Tropical Storm Bolaven is moving around the southern side of an upper level ridge centered east of the Philippines. The ridge is generating strong southeasterly winds which are blowing across the top of the circulation. Those winds are causing moderate vertical wind shear. The wind shear is probably the reason why most of the stronger storms are occurring northwest of the center of circulation. Although Bolaven will move over water where the Sea Surface Temperature is near 28°C, the vertical wind shear will likely prevent intensification. In fact if the shear increases, then Bolaven could weaken to a tropical depression.
The ridge north of Bolaven is steering the tropical storm toward the west-northwest and that general motion is expected to continue for several more days. On its anticipated track Tropical Storm Bolaven could reach the coast of South Vietnam in 24 to 36 hours. Bolaven will bring gusty winds and locally heavy rain to parts of southern Vietnam.