Tag Archives: Tropical Storm Bolaven

Tropical Storm Bolaven Moves Toward the Marianas

Tropical Storm Bolaven moved toward the Marianas on Sunday night. At 11:00 p.m. EDT on Sunday the center of Tropical Storm Bolaven was located at latitude 11.1°N and longitude 149.9°E which put it about 410 miles (660 km) east-southeast of Guam. Bolaven was moving toward the west-northwest at 10 m.p.h. (16 km/h). The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 80 m.p.h. (130 km/h). The minimum surface pressure was 992 mb.

A Typhoon Watch was in effect for Guam, Rota, Tinian and Saipan. A Tropical Storm Warning was also in effect for Guam.

Tropical Storm Bolaven strengthened on Sunday. The inner end of a rainband wrapped around the center of Bolaven’s circulation. Bands of showers and thunderstorms revolved around the center of circulation. Storms near the center generated upper level divergence that pumped mass away from the tropical storm. Winds to tropical storm force extended out 70 miles (100 km) from the center of Bolaven.

Tropical Storm Bolaven will move through an environment favorable for intensification during the next 24 hours. Bolaven will move over water where the Sea Surface Temperatures are near 30°C. It will move under the southern part of an upper level ridge over the Western North Pacific Ocean. The ridge will produce easterly winds that will blow toward the top of Bolaven’s circulation. Those winds will cause some vertical wind shear, but the wind shear will not be enough to prevent intensification. Tropical Storm Bolaven is likely to intensify to a typhoon during the next 24 hours.

Tropical Storm Bolaven will move around the southwestern part of a high pressure system over the Western North Pacific Ocean. The high pressure system will steer Bolaven toward the northwest during the next 24 hours. On its anticipated track Tropical Storm Bolaven will move closer to the Marianas. Bolaven could reach the Marianas in less than 36 hours. Bolaven will very likely be a typhoon when it reaches the Marianas.

Elsewhere over the Western North Pacific Ocean, former Typhoon Koinu made landfall on the coast of China west of Hong Kong on Sunday. At 11:00 p.m. EDT on Sunday the center of Tropical Storm Koinu was located at latitude 21.5°N and longitude 112.9°E which put it about 75 miles (120 km) west-southeast of Hong Kong. Koinu was moving toward the west at 5 m.p.h. (8 km/h). The maximum sustained wind speed was 70 m.p.h. (110 km/h) and there were wind gusts to 85 m.p.h. (135 km/h). The minimum surface pressure was 988 mb.

Typhoon Koinu Lingers Near Hong Kong

Typhoon Koinu lingered over the Western North Pacific Ocean near Hong Kong on Saturday. At 11:00 p.m. EDT on Saturday the center of Typhoon Koinu was located at latitude 21.4°N and longitude 114.4°E which put it about 65 miles (105 km) south-southeast of Hong Kong. Koinu was moving toward the west-northwest at 4 m.p.h. (6 km/h). The maximum sustained wind speed was 100 m.p.h. (160 km/h) and there were wind gusts to 120 m.p.h. (195 km/h). The minimum surface pressure was 968 mb.

Typhoon Koinu weakened gradually on Saturday as it lingered near Hong Kong. Since Koinu moved very slowly, the strong winds in the lower atmosphere mixed cooler water to the surface of the ocean. Koinu was unable to extract as much energy from the cooler water and the typhoon weakened. Thunderstorms in Typhoon Koinu did not rise quite as high into the atmosphere.

Even though Typhoon Koinu weakened on Saturday, it still exhibited a well organized circulation. A very small eye was present at the center of Koinu’s circulation. The inner end of a rainband wrapped around the existing eye and eyewall, and concentric eyewalls could be developing. Bands of showers and thunderstorms revolved around the small core of Typhoon Koinu. Storms near the core generated upper level divergence that pumped mass away from the typhoon.

The size of the circulation around Typhoon Koinu decreased as Koinu gradually weakened. Winds to typhoon force extended out 25 miles (40 km) from the center of Koinu’s circulation. Winds to tropical storm force extended out 90 miles (145 km) from the center of circulation. The Hurricane Intensity Index (HII) for Typhoon Koinu was 16.5. The Hurricane Size Index (HSI) was 8.6. and the Hurricane Wind Intensity Size Index (HWISI) was 25.1.

Typhoon Koinu will move through an environment somewhat unfavorable for intensification during the next 24 hours. Koinu will move over water where the Sea Surface Temperatures are near 27°C. It will move under axis of an upper level ridge over China. The upper level winds are weak near the axis of the ridge and there will be little vertical wind shear. However, strong winds in the lower atmosphere will continue to mix cooler water to the surface of the ocean. In addition, the circulation around the northern side of Typhoon Koinu could draw in some drier air from China. Typhoon Koinu is likely to continue to weaken gradually during the next 24 hours due to the mix of cooler water to the surface of the ocean.

Typhoon Koinu will move will move around the southern part of a high pressure system over eastern Asia. The high pressure system will steer Koinu slowly toward the west during the next 24 hours. On its anticipated track the center Typhoon Koinu will move south of Hong Kong on Sunday.

Elsewhere over the Western North Pacific Ocean, Tropical Depression 15W strengthened to Tropical Storm Bolaven east-southeast of Guam. At 11:00 p.m. EDT on Saturday the center of Tropical Storm Bolaven was located at latitude 9.6°N and longitude 152.9°E which put it about 630 miles (1020 km) east-southeast of Guam. Bolaven was moving toward the west-northwest at 5 m.p.h. (8 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. Typhoon Watches were in effect for Guam, Rota, Tinian and Saipan.

Tropical Storm Bolaven Forms Over the South China Sea

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.