Category Archives: Western North Pacific

Western Pacific Typhoons and Tropical Storms

Tropical Depression Forms East of the Philippines

A tropical depression formed over the Western North Pacific Ocean east of the Philippines on Saturday morning. At 7:00 a.m. EST on Saturday the center of a tropical depression was located at latitude 7.4°N and longitude 131.5°E which put it about 335 miles (540 km) east of Baganga, Philippines. The tropical depression was moving toward the west at 18 m.p.h. (30 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 1006 mb.

More thunderstorms formed near the center of a low pressure system over the Western North Pacific Ocean east of Mindanao on Saturday morning and the Japan Meteorological Agency designated the system as a tropical depression. Thunderstorms were occurring in bands in the western and northern sides of the tropical depression. Bands in the eastern and southern parts of the depression’s circulation consisted primarily of showers and lower clouds. Storms near the center of circulation generated upper level divergence that pumped mass away to the west of the tropical depression.

The tropical depression will move through an environment somewhat favorable for intensification during the next 24 hours. The tropical depression will move over water where the Sea Surface Temperatures are near 29°C. It will move under the southern part of an upper level ridge over the Western North Pacific Ocean east of the Philippines. The upper level ridge will produce easterly winds that will blow toward the top of the depression’s circulation. Those winds will cause moderate vertical wind shear. The vertical wind shear will inhibit intensification, but the shear may not be enough to stop intensification. The tropical depression could strengthen to a tropical storm, if the upper level winds do not get any stronger.

The tropical depression will move around the southern side of a high pressure system over the Western North Pacific Ocean and East Asia. The high pressure system will steer the tropical depression toward the west. On its anticipated track the tropical depression will reach Mindanao in less than 24 hours. The tropical depression will bring gusty winds and locally heavy rain to Mindanao. Heavy rain could cause flash floods in some locations.

Tropical Depression Forms Southeast of Yap

A tropical depression formed over the Western North Pacific Ocean southeast of Yap on Sunday morning. At 10:00 a.m. EST on Sunday the center of Tropical Depression 17W was located at latitude 7.2°N and longitude 139.9°E which put it about 205 miles (320 km) southeast of Yap. The tropical depression was moving toward the west-northwest at 11 m.p.h. (17 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 1003 mb.

More thunderstorms formed in a low pressure system over the Western North Pacific Ocean southeast of Yap on Sunday morning and both the Japan Meteorological Agency and the U.S. Joint Typhoon Warning Center designated the system as a tropical depression. The distribution of thunderstorms in Tropical Depression 17W was asymmetrical. Thunderstorms were occurring in bands in the western half of the tropical depression. Bands in the eastern side of Tropical Depression 17W consisted primarily of showers and lower clouds.

Tropical Depression 17W was moving under the southern part of an upper level ridge over the Western North Pacific Ocean. The upper level ridge was producing easterly wind that were blowing toward the top of the tropical depression’s circulation. Those winds were causing moderate vertical wind shear. The moderate vertical wind shear was causing the asymmetrical distribution of thunderstorms.

Tropical Depression 17W will move through an environment somewhat favorable for intensification during the next 48 hours. The tropical depression will move over water where the Sea Surface Temperatures are near 29°C. However, the upper level ridge over the Western North Pacific will continue to cause moderate vertical wind shear. The wind shear will inhibit intensification, but the shear probably will not be strong enough to prevent some strengthening. Tropical Depression 17W is likely to gradually intensify to a tropical storm during the next 48 hours.

Tropical Depression 17W will move south of an upper high pressure system over the Western North Pacific Ocean. The high pressure system will steer the tropical depression toward the west during the next 48 hours. On its anticipated track, Tropical Depression 17W will move south of Yap.

Tropical Storm Sanba Drops Heavy Rain on Southern China

Tropical Storm Sanba dropped heavy rain on parts of southern China on Thursday. At 5:00 p.m. EDT on Thursday the center of Tropical Storm Sanba was located at latitude 21.3°N and longitude 109.2°E which put it about 25 miles (40 km) southeast of Beihai China. Sanba was moving toward the north-northeast at 8 m.p.h. (13 km/h). The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h). The minimum surface pressure was 1001 mb.

Tropical Storm Sanba dropped heavy rain on parts of Guangxi and Guangdong in southern China on Thursday. The center of Sanba’s circulation was still over the northeastern Gulf of Tonkin. Much of the northern half of Tropical Storm Sanba was over southern China. Part of the eastern side of Sanba’s circulation was over Hainan. Winds to tropical storm force extended out 60 miles (95 km) from the center of Tropical Storm Sanba.

An upper level trough over eastern Asia and an upper level ridge centered north of the Philippines were interacting to produce southwesterly winds that were blowing toward the top of Sanba’s circulation. Those winds were causing moderate vertical wind shear and they were also causing the distribution of thunderstorms to be asymmetrical. Thunderstorms were occurring in bands in the northern and eastern parts of Tropical Storm Sanba. Bands in the southern and western parts of Sanba’s circulation consisted primarily of showers and lower clouds.

Tropical Storm Sanba will be in an environment that is mostly unfavorable for intensification during the next 24 hours. Sanba will move over water where the Sea Surface Temperatures are near 28°C. The upper level trough over eastern Asia and the upper level ridge north of the Philippines will continue to cause moderate vertical wind shear. Almost half of Sanba’s circulation will be over land and increased friction will slow the wind in those areas. Tropical Storm Sanba is likely to weaken during the next 24 hours even if the center of circulation does not move over southern China.

The movement of Tropical Storm Sanba during the next 24 hours will depend on how strong the vertical wind shear is. If the wind shear is moderate and the upper and lower parts of Sanba’s circulation remain connected, then southwesterly winds will steer Tropical Storm Sanba toward the north-northeast. If Sanba moves north-northeast it will move inland over southern China. If the vertical wind shear gets stronger, then the upper level winds will push the top part of Sanba’s circulation toward the north-northeast. If the wind shear rips the top off of Tropical Storm Sanba, then the lower part of the circulation could meander over the northeastern Gulf of Tonkin during the next 24 hours.

Tropical Storm Sanba will continue to drop heavy rain over southern China during the next 24 hours. Heavy rain will fall on parts of Guangxi and Guangdong. Prolonged heavy rain will cause floods in some locations.

Tropical Storm Sanba Forms East of Vietnam

Tropical Storm Sanba formed over the Gulf of Tonkin east of Vietnam on Wednesday. At 11:00 a.m. EDT on Wednesday the center of Tropical Storm Sanba was located at latitude 18.9°N and longitude 108.2°E which put it about 180 miles (280 km) southeast of Haiphong, Vietnam. Sanba was moving toward the northwest at 9 m.p.h. (15 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 1003 mb.

A low pressure system over the Gulf of Tonkin east of Vietnam strengthened on Wednesday and the Japan Meteorological Agency designated the system as Tropical Storm Sanba. The distribution of thunderstorms in Tropical Storm Sanba was asymmetrical. Many of the thunderstorms were occurring in bands in the eastern side of Sanba’s circulation. Bands in the western part of Tropical Storm Sanba consisted primarily of showers and lower clouds. Storms near the center of Sanba’s circulation generated upper level divergence that pumped mass away to the west and north of the tropical storm. Winds to tropical storm force extended out 50 miles (80 km) in the eastern side of Tropical Storm Sanba. The winds in the western part of Sanba’s circulation were blowing at less than tropical storm force.

Tropical Storm Sanba will move through an environment somewhat favorable for intensification during the next 24 hours. Sanba will move over water where the Sea Surface Temperatures are near 28°C. It will move under the western part of an upper level ridge centered northwest of the Philippines. The upper level ridge will produce southeasterly winds that will blow toward the top of Sanba’s circulation. Those winds will cause some vertical wind shear but the wind shear will not be strong enough to prevent intensification. Some of the air circulating around the eastern side of Tropical Storm Sanba will flow over Hainan. The additional friction caused by the land will cause the air in that part of Sanba’s circulation to slow down. Tropical Storm Sanba could intensify gradually during the next 24 hours.

Tropical Storm Sanba will move around the western part of a high pressure system over the Western North Pacific Ocean. The high pressure system will steer Sanba toward the north-northwest during the next 24 hours. On its anticipated track the center of Tropical Cyclone Sanba will pass west of Hainan. Sanba will move toward northeastern Vietnam.

Bands in the eastern side of Tropical Storm Sanba are already producing gusty winds and locally heavy rain in parts of Hainan. Bands in the western side of Sanba’s circulation are bringing rain showers to parts of northern Vietnam. Tropical Storm Sanba will continue to produce gusty winds and locally heavy rain in parts of Hainan and northern Vietnam. Heavy rain could cause flash floods in some locations.

Typhoon Bolaven Passes East of Iwo To

Typhoon Bolaven passed east of Iwo To on Thursday evening. At 11:00 p.m. EDT on Thursday the center of Typhoon Bolaven was located at latitude 26.2°N and longitude 147.8°E which put it about 350 miles (570 km) east of Iwo To. Bolaven was moving toward the northeast at 23 m.p.h. (37 km/h). The maximum sustained wind speed was 145 m.p.h. (235 km/h) and there were wind gusts to 175 m.p.h. (285 km/h). The minimum surface pressure was 928 mb.

Concentric eyewalls developed at the center of Typhoon Bolaven on Thursday. The inner end of a rainband wrapped around the existing small eye and eyewall. The larger outer eyewall surrounded the inner eye and eyewall. Bands of showers and thunderstorms revolved around the concentric eyewalls. Storms near the eyewalls generated upper level divergence that pumped mass away to the northeast of the typhoon.

The size of Typhoon Bolaven increased when the concentric eyewalls developed. Winds to typhoon force extended out 60 miles (95 km) from the center of Bolaven’s circulation. Winds to tropical storm force extended out 265 miles (425 km) from the center of circulation. The Hurricane Intensity Index (HII) for Typhoon Bolaven was 29.9. The Hurricane Size Index (HSI) was 21.3 and the Hurricane Wind Intensity Size Index (HWISI) was 51.2.

Typhoon Bolaven will move through an environment that will become more unfavorable for a powerful typhoon during the next 24 hours. Bolaven will move over water where the Sea Surface Temperatures are near 27°C. It will move under the eastern side of an upper level trough near Japan. The upper level trough will produce southwesterly winds that will blow toward the top of Bolaven’s circulation. Those winds will cause the vertical wind shear to increase. Typhoon Bolaven is likely to weaken during the next 24 hours as it goes through an eyewall replacement cycle and the vertical wind shear increases. Bolaven could make a transition to a strong extratropical cyclone when it moves over cooler water south of Alaska.

The upper level trough near Japan will steer Typhoon Bolaven quickly toward the northeast during the next 24 hours. On its anticipated track, Typhoon Bolaven will pass far to the east of Japan on Friday. Bolaven could move south of the Aleutian Islands during the weekend.

Typhoon Bolaven Gets Even Stronger

Typhoon Bolaven got even stronger on Wednesday morning. At 11:00 a.m. EDT on Wednesday the center of Typhoon Bolaven was located at latitude 19.3°N and longitude 142.9°E which put it about 420 miles (675 km) south-southeast of Iwo To. Bolaven was moving toward the northwest at 9 m.p.h. (15 km/h). The maximum sustained wind speed was 180 m.p.h. (290 km/h) and there were wind gusts to 220 m.p.h. (355 km/h). The minimum surface pressure was 904 mb.

Typhoon Bolaven grew even more powerful on Wednesday morning. A circular eye with a diameter of 16 miles (26 km) was at the center of Bolaven’s circulation. The eye was surrounded by a ring of thunderstorms and the strongest winds were occurring in that ring of storms. Bands of showers and thunderstorms were revolving around the core of Typhoon Bolaven. Storms near the core generated strong upper level divergence that pumped large quantities of mass away from the typhoon. The removal of large amounts of mass caused the surface pressure to decrease to 904 mb.

The circulation around Typhoon Bolaven was very symmetrical. Winds to typhoon force extended out 45 miles (65 km) from the center of Bolaven’s circulation. Winds to tropical storm force extended out 195 miles (315 km) from the center of circulation. The Hurricane Intensity Index (HII) for Typhoon Bolaven was 42.2. The Hurricane Size Index (HSI) was 18.4 and the Hurricane Wind Intensity Size Index (HWISI) was 60.6. Typhoon Bolaven was similar in intensity to Hurricane Dorian in 2019. Bolaven was bigger than Dorian was.

Typhoon Bolaven will move through an environment favorable for a very powerful typhoon during the next 24 hours. Bolaven will move over water where the Sea Surface Temperatures are near 30°C. It will move through a region where the upper level winds are weak and there will be little vertical wind shear. Typhoon Bolaven could maintain its intensity during the next 24 hours. If the inner end of a rainband wraps around the existing eye and eyewall, then concentric eyewalls could form. If concentric eyewalls form, then an eyewall replacement cycle could cause Typhoon Bolaven to weaken.

Typhoon Bolaven will move around the western part of a high pressure system over the Western North Pacific Ocean. The high pressure system will steer Bolaven toward the north during the next 24 hours. On its anticipated track, the Typhoon Bolaven will move closer to Iwo To.

Typhoon Bolaven Rapidly Intensifies to Equivalent of Cat. 5 Hurricane

Typhoon Bolaven rapidly intensified to the equivalent of a Category 5 hurricane on the Saffir-Simpson Scale on Tuesday evening. At 11:00 p.m. EDT on Tuesday the center of Typhoon Bolaven was located at latitude 17.5°N and longitude 143.8°E which put it about 245 miles (390 km) north-northwest of Guam. Bolaven was moving toward the north-northwest at 14 m.p.h. (22 km/h). The maximum sustained wind speed was 160 m.p.h. (260 km/h) and there were wind gusts to 185 m.p.h. (295 km/h). The minimum surface pressure was 920 mb.

Typhoon Warnings were in effect for Rota, Tinian and Saipan. Tropical Storm Warnings were in effect for Agrihan, Pagan and Alamagan.

Typhoon Bolaven rapidly intensified to the equivalent of a Category 5 hurricane west of the Marianas on Tuesday evening. A small circular eye with a diameter of 14 miles (22 km) was at the center of Bolaven’s circulation. The eye was surrounded by a ring of thunderstorms and the strongest winds were occurring in that ring of storms. Bands of showers and thunderstorms were revolving around the core of Typhoon Bolaven. Storms near the core generated upper level divergence that pumped mass away from the typhoon.

The circulation around Typhoon Bolaven was very symmetrical. Winds to typhoon force extended out 25 miles (40 km) from the center of Bolaven’s circulation. Winds to tropical storm force extended out 185 miles (295 km) from the center of circulation. The Hurricane Intensity Index (HII) for Typhoon Bolaven was 35.0. The Hurricane Size Index (HSI) was 11.5 and the Hurricane Wind Intensity Size Index (HWISI) was 46.5.

Typhoon 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 through a region where the upper level winds are weak and there will be little vertical wind shear. Typhoon Bolaven could continue to intensify during the next 24 hours. If the inner end of a rainband wraps around the existing eye and eyewall, then concentric eyewalls could form. If concentric eyewalls form, then an eyewall replacement cycle could cause Typhoon Bolaven to weaken.

Typhoon Bolaven will move around the western part of a high pressure system over the Western North Pacific Ocean. The high pressure system will steer Bolaven toward the north-northwest during the next 24 hours. On its anticipated track, the Typhoon Bolaven will stay west of the Marianas during the next 24 hours.

Typhoon Bolaven Rapidly Intensifies to Equivalent of a Major Hurricane

Typhoon Bolaven rapidly intensified to the equivalent of a major hurricane over the Western North Pacific Ocean north of Guam on Tuesday. At 5:00 p.m. EDT on Tuesday the center of Typhoon Bolaven was located at latitude 16.4°N and longitude 144.3°E which put it about 100 miles (160 km) northwest of Tinian. Bolaven was moving toward the north-northwest at 11 m.p.h. (17 km/h). The maximum sustained wind speed was 115 m.p.h. (185 km/h) and there were wind gusts to 145 m.p.h. (230 km/h). The minimum surface pressure was 959 mb.

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

Typhoon Bolaven brought strong winds and heavy rain to Guam, Rota, Tinian and Saipan. The center of Bolaven passed between Rota and Tinian and the strongest winds likely occurred in those places. A weather station in Saipan reported a sustained wind speed of 49 m.p.h. (79 km/h) and a wind gust of 68 m.p.h. (110 km/h). A weather station at Guam International Airport reported a sustained wind speed of 32 m.p.h. (52 km/h) and a wind gust of 46 m.p.h. (74 km/h). That weather station also measured 4.54 inches (115.3 mm) of rain.

Typhoon Bolaven began to intensify rapidly as it moved west of the Marianas. A small circular eye with a diameter of 14 miles (22 km) developed at the center of Bolaven’s circulation. The eye was surrounded by a ring of thunderstorms and the strongest winds were occurring in that ring of storms. Bands of showers and thunderstorms were revolving around the core of Typhoon Bolaven. Storms near the core generated upper level divergence that pumped mass away from the typhoon.

The size of the circulation around Typhoon Bolaven increased when it intensified on Tuesday. Winds to typhoon force extended out 25 miles (40 km) from the center of Bolaven’s circulation. Winds to tropical storm force extended out 185 miles (295 km) from the center of circulation. The Hurricane Intensity Index (HII) for Typhoon Bolaven was 20.6. The Hurricane Size Index (HSI) was 11.5 and the Hurricane Wind Intensity Size Index (HWISI) was 32.1.

Typhoon 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 through a region where the upper level winds are weak and there will be little vertical wind shear. Typhoon Bolaven will intensify during the next 24 hours. Bolaven could intensify rapidly at times. Typhoon Bolaven could strengthen to the equivalent of a Category 5 hurricane on the Saffir-Simpson Scale.

Typhoon Bolaven will move around the western part of a high pressure system over the Western North Pacific Ocean. The high pressure system will steer Bolaven toward the north-northwest during the next 24 hours. On its anticipated track, the Typhoon Bolaven will stay west of the Marianas during the next 24 hours.

Bolaven Strengthens to a Typhoon East of Guam

Former Tropical Storm Bolaven strengthened to a typhoon east of Guam on Monday night. At 11:00 p.m. EDT on Monday the center of Typhoon Bolaven was located at latitude 14.0°N and longitude 146.0°E which put it about 110 miles (175 km) east of Guam. Bolaven was moving toward the northwest at 12 m.p.h. (19 km/h). The maximum sustained wind speed was 80 m.p.h. (130 km/h) and there were wind gusts to 100 m.p.h. (160 km/h). The minimum surface pressure was 990 mb.

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

Former Tropical Storm Bolaven strengthened to a typhoon as it neared the Marianas on Monday night. A circular eye formed at the center of Bolaven’s circulation. The eye was surrounded by a ring of thunderstorms and the strongest winds were occurring in that ring of storms. Bands of showers and thunderstorms were revolving around the core of Typhoon Bolaven. Storms near the core generated upper level divergence that pumped mass away from the typhoon.

The size of the circulation around Bolaven increased when it intensified on Monday. Winds to typhoon force extended out 35 miles (55 km) from the center of Bolaven’s circulation. Winds to tropical storm force extended out 140 miles (220 km) from the center of circulation.

Typhoon 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 through a region where the upper level winds are weak and there will be little vertical wind shear. Typhoon Bolaven will intensify during the next 24 hours. Bolaven could intensify rapidly at times.

Typhoon 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, the center Typhoon Bolaven will pass near Rota in a few hours.

Typhoon Bolaven will bring strong winds and heavy rain to Rota, Tinian and Saipan. The strongest winds are likely to occur in Rota and Tinian. Bolaven will also produce gusty winds and heavy rain in Guam. The strong winds will be capable of causing damage and electricity outages are likely. Heavy rain will cause flash floods in some locations.

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.