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.
More thunderstorms developed on Saturday around the circulation previously designated Tropical Depression 01W earlier this week when it moved through the southern Philippines. At 10:00 p.m. EST the center of Tropical Depression 01W was located at latitude 9.4°N and longitude 109.1°E which put it about 220 miles (355 km) east-southeast of Ho Chi Minh City, Vietnam. The depression was moving toward the west at 6 m.p.h. (10 km/h). The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h). The minimum surface pressure was 1002 mb.
After persisting mainly as a low level circulation during the past few days as it moved westward across the South China Sea, more thunderstorms developed in the depression on Saturday. Most of the thunderstorms developed in bands north and west of the center of circulation. There were bands of low clouds and showers in the southeastern portion of the circulation. The depression has a well defined low level center of circulation. Thunderstorms were starting to generate some upper level divergence which was pumping mass away to the northwest of the depression.
The depression will be moving through an environment that is marginal for intensification. It will be moving over water where the Sea Surface Temperature is near 26°C to 27°C. So, there will be enough energy in the upper ocean to support intensification. An upper level ridge to the east of the depression is generating southeasterly winds which are blowing across the top of the circulation. The moderate vertical wind shear will inhibit intensification. If the shear does not increase, the depression could maintain its intensity or strengthen slightly during the next 24 hours.
A ridge north of the depression is steering it toward the west and that general motion is expected to continue for another day or two. On its anticipated track the depression will move toward the southernmost part of Vietnam. The depression could bring locally heavy rain to southern Vietnam. The rain could be heavy enough to cause flooding in some areas.
A center of circulation formed within a cluster of thunderstorms east of Mindanao on Saturday and the system was designated Tropical Depression 01W. At 10:00 p.m. EST on Saturday the center of Tropical Depression 01W was located at latitude 9.2°N and longitude 126.5°E which put it about 200 miles (320 km) east-southeast of Cebu, Philippines. The depression was moving toward the northwest at 10 m.p.h. The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h). The minimum surface pressure was 1000 mb.
Although there is a distinct center of circulation in Tropical Depression 01W, the distribution of thunderstorms is asymmetrical. Most of the stronger thunderstorms are forming in the northern half of the circulation and there are few thunderstorms in the southern half of the circulation. The thunderstorms in the northern half of the circulation are generating upper level divergence that is pumping out mass toward the northeast and northwest of the tropical depression.
Tropical Depression 01W will be moving through an oceanic and atmospheric environment that is somewhat favorable for intensification. It will move over water where the Sea Surface Temperature is near 28°C. An upper level ridge is generating southeasterly winds which are blowing across the top of the depression, but the vertical wind shear is not too strong. However, the center of Tropical Depression 01W will move over some of the islands of the southern Philippines. Increases friction and high topography will disrupt the circulation each time the center moves over land. The intermittent passages overland will cause weakening and the intensity of Tropical Depression 01W is likely to fluctuate during the next several days.
A subtropical ridge north of the depression is steering it toward the northwest. The ridge is forecast to strengthen and it is predicted to steer Tropical Depression 01W in a general westerly direction during the next several days. On its anticipated track the center of Tropical Depression 01W will pass near northern Mindanao, Siargao Island, Dinogat Island, Leyte, Bohol Island, Cebu, Negros, and Panay Island.
Heavy rain associated will be the greatest threat with Tropical Depression 01W. The heaviest rain will fall north of where the center moves. The heavy rain could cause flooding and mudslides,