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.
Tropical Storm Tembin strengthened into a typhoon on Saturday as it moved over the South China Sea. At 10:00 p.m. EST on Saturday the center of Typhoon Tembin was located at latitude 8.2°N and longitude 113.6°E which put it about 540 miles (880 km) east of Ho Chi Minh City, Vietnam. Tembin was moving toward the west at 18 m.p.h. (29 km/h). The maximum sustained wind speed was 85 m.p.h. (135 km/h) and there were wind gusts to 105 m.p.h. (170 km/h). The minimum surface pressure was 976 mb.
Typhoon Tembin became much better organized on Saturday. A primary rainband wrapped around the center of circulation and an eye became apparent on microwave satellite imagery. Several other rainbands strengthened outside the core of Typhoon Tembin. Storms near the core of the circulation generated strong upper level divergence which pumped mass away to the west and northeast of the typhoon. The removal of mass allowed the surface pressure to decrease and the wind speed to increase. Winds to typhoon force extended out about 40 miles (65 km) from the center of circulation. Winds to tropical storm force extended out about 155 miles (250 km) from the center.
Typhoon Tembin will move through an environment favorable for intensification during the next 24 hours. Tembin will move over water where the Sea Surface Temperature is near 29°C. An upper level ridge north of Tempin is producing easterly winds which are blowing toward the typhoon. However, the easterly winds are blowing at most levels of the atmosphere and there is not a lot of vertical wind shear. Typhoon Tembin is likely to continue to intensify on Sunday.
The subtropical ridge north of Tembin is steering the typhoon quickly toward the west. A general motion toward the west is expected to continue. On its anticipated track Typhoon Tembin could approach the southern part of Vietnam in about 36 hours. Tembin has the potential to bring strong winds, heavy rain and a storm surge to the southern coast of Vietnam.
Tropical Storm Kai-tak weakened as it passed over the Philippines. Kai-tak dropped heavy rain which caused floods and mudslides before it weakened. At 10:00 p.m. EST on Sunday the center of Tropical Storm Kai-tak was located at latitude 10.5°N and longitude 119.1°E which put it about 75 miles (120 km) northeast of Puerto Princesa, Philippines. Kai-tak was moving toward the west-southwest 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.
Moving over islands of the central Philippines disrupted parts of the circulation of Tropical Storm Kai-tak. In addition an upper level ridge produced strong easterly winds which blew across the top of the circulation. Those winds caused moderate vertical wind shear. The strong upper level winds periodically weakened the thunderstorms near the core of the circulation. The upper level winds slowed at times and more storms developed near the center of Tropical Storm Kai-tak. The persistent vertical wind shear weakened the low level circulation.
More thunderstorms developed near the center of Tropical Storm Kai-tak during recent hours, but the circulation remains asymmetrical. The new storms were forming west of the center of circulation. There were only a few thin bands of showers in the eastern half of the circulation. The strongest winds were occurring in the thunderstorms west of the center of Tropical Storm Kai-tak. The Japan Meteorological Agency was maintaining a classification of a tropical storm.
Tropical Storm Kai-tak will move through an environment only marginally favorable for intensification. Kai-tak will move over water where the Sea Surface Temperature is near 29°C. The upper level ridge will continue to produce strong easterly winds and there will continue to be moderate vertical wind shear. Tropical Storm Kai-tak could maintain its intensify, if the wind shear does not increase. However, if the upper level winds get stronger, then they could blow the top off of the circulation.
Tropical Storm Kai-tak is moving south of a subtropical ridge which is steering the tropical storm toward the west-southwest. The west-southwesterly motion is forecast to continue for another day or two. On its anticipated track Tropical Storm Kai-tak will move across Palawan and over the South China Sea.