Category Archives: Western North Pacific

Western Pacific Typhoons and Tropical Storms

Tropical Depression 04W Forms East of the Northern Marianas

Tropical Depression 04W formed east of the Northern Marianas very late on Friday.  At 11:00 p.m. EDT on Friday the center of Tropical Depression 04W was located at latitude 18.8°N and longitude 148.5°E which put it about 185 miles (300 km) east of Agrihan.  It was moving toward the 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.

An area of showers and thunderstorms persisted for much of the past week east of the Northern Marianas.  Several smaller centers of circulation formed within the area of showers and storms, but those centers ran into strong upper level winds and weakened because strong vertical wind shear and they dissipated.  Another center formed on Friday, but the upper level winds were a little weaker and the center persisted.  An upper level trough south of Japan was still producing southwesterly winds which were blowing toward the top of the circulation.  Those winds were producing moderate vertical wind shear, but the center of circulation persisted.  Most of the thunderstorms were occurring in bands east of the center of circulation.  The bands west of the center consisted primarily of low clouds and showers.

Tropical Depression will move through an area marginally favorable for intensification during the next 24 hours.  it will move over water where the Sea Surface Temperatures are near 28°C.  So, there will be enough energy in the upper ocean to support some intensification.  The upper level trough south of Japan will continue to cause moderate vertical wind shear, but the upper level winds could be weak enough to allow for further intensification.  Tropical Depression 04W could strengthen into a tropical storm on Saturday.

Tropical Depression 04W is moving near the southwestern part of a ridge over the North Pacific Ocean.  The ridge is steering the depression toward the northwest and that general motion is expected to continue for another day or two.  On its anticipated track Tropical Depression 04W is expected to pass near the northernmost Mariana Islands.  It could pass near Asuncion Island, the Maug Islands, Supply Reef and Farallon de Pajaros.  Tropical Depression 04W could bring gust winds, locally heavy rain and higher waves to those places.

Tropical Storm Jelawat Weakens Rapidly Over the Northern Marianas

Tropical Storm Jelawat weakened rapidly over the Northern Marianas on Saturday.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Jelawat was located at latitude 19.3°N and longitude 145.5°E which put it about 50 miles (80 km) north-northwest of Agrihan.  Jelawat was moving toward the east-northeast at 14 m.p.h. (22 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 993 mb.

Former Typhoon Jelawat moved into an area where there were upper level westerly winds blowing at 50 m.p.h. (80 km/h).  Those strong upper level winds created enough vertical wind shear to blow the upper two thirds of the circulation east of the lower part of the circulation.  The remaining strong thunderstorms were weakening well to the east of the lower level circulation.  Tropical Storm Jelawat consisted primarily of narrow bands of showers and low clouds that were revolving around the center of circulation.  Jelawat may bring brief gusty winds and showers to the northernmost islands in the Marianas.

Typhoon Jelawat Rapidly Intensifies Into Equivalent of Major Hurricane

Typhoon Jelawat intensified rapidly on Friday into the equivalent of a major hurricane.  At 11:00 a.m. EDT on Friday the center of Typhoon Jelawat was located at latitude 17.1°N and longitude 139.5°E which put it about 440 miles (710 km) northwest of Guam.  Jelawat was moving toward the east-northeast at 13 m.p.h. (21 km/h).  The maximum sustained wind speed was 150 m.p.h. (240 km/h) and there were wind gusts to 185 m.p.h. (295 km/h).  The minimum surface pressure was 926 mb.

Typhoon Jelawat intensified rapidly on Friday.  There was a small circular eye at the center of circulation.  A ring of very strong storms surrounded the eye and the strongest winds were occurring in that ring of storms.  Several spiral bands were revolving around the core of the circulation.  Storms near the core were generating well developed upper level divergence which was pumping large quantities of mass away to the east of the typhoon.  The removal of mass allowed the surface pressure to decrease rapidly and that produced a a rapid increase in wind speed.

Winds to typhoon force extend out about 45 miles (75 km) from the center of Typhoon Jelawat.  Winds to tropical storm force extend out about 175 miles (280 km) from the center of circulation.  The Hurricane Intensity Index (HII) for Typhoon Jelawat is 31.6.  The Hurricane Size Index (HSI) is 17.7 and the Hurricane Wind Intensity Size Index (HWISI) is 49.3.

Typhoon Jelawat is in an environment favorable for strong typhoons, but it may be near its peak in intensity.  Jelawat will move over water where the Sea Surface Temperature is near 28°C.  Typhoon Jelwat has moved around the western end of an upper level ridge which is producing easterly winds that are blowing toward the top of the circulation.  The winds are causing some vertical wind shear, but the shear has not inhibited intensification.  When Typhoon Jelawat moves farther to the northeast it will move under stronger easterly and the wind shear will increase.  More shear will cause Jelawat to weaken during the next few days.

A subtropical ridge to the east of Typhoon Jelawat is steering the typhoon toward the east-northeast.  A general motion toward the east-northeast is expected to continue for several more days.  On its anticipated track Typhoon Jelawat could approach the northernmost islands in the Marianas in about 48 hours.

Typhoon Jelawat Strengthens West-Northwest of Guam

Former Tropical Storm Jelawat strengthened into a typhoon as it moved west-northwest of Guam on Thursday.  At 11:00 p.m. EDT on Thursday the center of Typhoon Jelawat was located at latitude 15.9°N and longitude 137.7°E which put it about 520 miles (840 km) west-northwest of Guam.  Jelawat was moving toward the east-northeast at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 90 m.p.h. (145 km/h) and there were wind gusts to 115 m.p.h. (185 km/h).  The minimum surface pressure was 972 mb.

Typhoon Jelawat strengthened quickly on Thursday night.  A small eye developed at the center of circulation.  A ring of strong thunderstorms surrounded the eye and the strongest winds were occurring in that ring of storms.  Several bands of showers and thunderstorms were revolving around the core of Typhoon Jelawat.  Storms in the core of the circulation were generating upper level divergence which was pumping mass away to the northeast of the typhoon.  Winds to typhoon force extended out about 45 miles (75 km) from the center of circulation.  Winds to tropical storm force extended out about 145 miles (230 km) from the center.

Typhoon Jelawat will move through an area favorable for intensification on Friday.  Jelawat will move over water where the Sea Surface Temperature is near 28°C.  Typhoon Jelawat has moved around the western end of an upper level ridge which is producing southwesterly winds which are blowing toward the top of the circulation.  Those winds are producing some vertical wind shear, but the wind shear is not strong enough to prevent intensification.   Typhoon Jelwat is likely to intensify further on Friday.

The upper level ridge is steering Typhoon Jelawat toward the east-northeast and that general motion is expected to continue for several more days.  On its anticipated track Typhoon Jelawat is expected to pass northwest of Guam.  Jelawat could approach the northernmost islands in the Marianas in about two or three days.

Tropical Storm Jelawat Strengthens West of Guam

Tropical Storm Jelawat strengthened west of Guam late on Tuesday.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Jelawat was located at latitude 12.3°N and longitude 135.5°E which put it about 230 miles (375 km) northwest of Yap and about 600 miles (970 km) west of Guam.  Jelawat was moving toward the north at 10 m.p.h. (16 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 994 mb.

After being affected by strong vertical wind shear for about 36 hours, Tropical Storm Jelawat began to strengthen late on Tuesday.  Many more thunderstorms formed near the center of circulation.  The circulation became much more symmetrical.  Bands of showers and thunderstorms formed in all parts of the circulation.  The storms near the center of circulation started to generate upper level divergence which pumped mass away from the tropical storm.

Tropical Storm Jelawat will be moving through an environment favorable for intensification during the next several days.  Jelawat will move over water where the Sea Surface Temperature is near 28°C.  Tropical Storm Jelawat is moving around the western end of an upper level ridge.  The ridge is producing southerly winds which are blowing toward the tropical storm.  The winds are producing some vertical wind shear, but the shear is not as strong as it has been.  Tropical Storm Jelawat will intensify during the next day or two and it could strengthen into a typhoon.

The ridge is steering Tropical Storm Jelawat toward the north and the northerly motion is expected to continue for another 12 to 24 hours.  Jelawat will move more toward the northeast in a day or so after it rounds the western end of the ridge.  On its anticipated track Tropical Storm Jelawat will move away from Yap and it will remain west of Guam.

Tropical Storm Jelawat Forms Near Yap

Tropical Storm Jelawat formed near Yap on Sunday.  At 2:00 p.m. EDT on Sunday the center of Tropical Storm Jelawat was located at latitude 7.6°N and longitude 138.4°E which put it about 120 miles (195 km) south of Yap.  Jelawat was moving toward the northwest at 14 m.p.h. (22 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 998 mb.

A low level center of circulation formed near the eastern edge of a cluster of thunderstorms near Yap on Sunday and the Japan Meteorological Agency designated the system as Tropical Storm Jelawat.  Tropical Storm Jelawat does not have a well organized circulation.  There is a distinct low level center of circulation, but most of the stronger thunderstorms are occurring west of the center of circulation.  The bands in the eastern half of the circulation consist mainly of showers and low clouds.  An upper level ridge over the Central North Pacific Ocean is producing strong easterly winds which are blowing across the top of the circulation.  Those winds are generating strong vertical wind shear and the shear is the main reason for the asymmetrical distribution of storms.

Tropical Storm Jelawat will be moving through an environment that is somewhat favorable for intensification.  Jelawat will move over water where the Sea Surface Temperature is near 28°C.  However, the upper level ridge will continue to cause vertical wind shear.  If the shear is not too strong and the circulation remains vertically coherent, then Tropical Storm Jelawat could strengthen during the next several days.   Some models predict this scenario and forecast that Jelawat will intensify into a typhoon.  Alternatively, if the wind shear increases further, strong upper level winds could blow the upper half of the circulation away from the lower level circulation.  If that occurs, Tropical Storm Jelawat will weaken.

The ridge over the Central North Pacific is steering Tropical Storm Jelawat toward the northwest.  Jelawat will reach the western end of the ridge in 12 to 24 hours.  The tropical storm will turn more toward the north when it reaches the end of the ridge.  On its anticipated track the center of Tropical Storm Jelawat is forecast to pass between Yap and Palau.

Tropical Storm Sanba Brings Rain to the Southern Philippines

Tropical Storm Sanba brought rain to the southern Philippines on Monday.  At 10:00 p.m. EST on Monday the center of Tropical Storm Sanba located at latitude 9.9°N and longitude 125.1°E which put it about 100 miles (160 km) east of Cebu, Philippines.  Sanba was moving toward the west-northwest at 19 m.p.h. (31 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.

Tropical Storm Sanba dropped locally heavy rain on parts of northern Mindanao, Siriagao Island, Dinegat Island, Leyte, southern Samar, Bohol and Cebu on Monday.  The circulation of Tropical Storm Sanba was not well organized.  Bands of showers and thunderstorms were occurring to the north and west of the center of circulation.  There were thin bands of showers and low clouds to the south and east of the center.  An upper level ridge to the north of Sanba was producing easterly winds which were blowing over the top of the circulation.  Those winds were causing moderate vertical wind shear which was the primary reason for the asymmetrical distribution of thunderstorms.

Tropical Storm Sanba will move through an environment marginal for intensification.  Sanba will move over water where the Sea Surface Temperature is near 28°C.  The upper level ridge will continue to produce moderate vertical wind shear, which will inhibit intensification.  In addition, the center of circulation will move across Cebu and Negros.  Increased friction caused by the and could weaken Tropical Storm Sanba.  Sanba could intensify a little when the center moves over the Sulu Sea.

A ridge north of Sanba is steering the tropical storm toward the west.  A general motion toward the west is expected to continue for another 24 to 36 hours.  After that time Sanba could move a little more toward the west-northwest.  On its anticipated track Tropical Storm Sanba is forecast to move over Cebu and Negros during the next 12 to 18 hours.  Sanba will move across the Sulu Sea toward Palawan and over the South China Sea.  Tropical Storm Sanba could drop locally heavy rain over Cebu, Negros, Panay and Palawan.  Prolonged heavy rain could cause flooding in some places.

Tropical Storm Sanba Develops Near Palau

Tropical Storm Sanba developed near Palau on Sunday.  At 10:00 a.m. EST on Sunday the center of Tropical Storm Sanba was located at latitude 7.2°N and longitude 133.5°E which put it about 20 miles (35 km) south-southwest of Koror, Palau.  Sanba was moving toward the west at 19 m.p.h. (31 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.

Thunderstorms developed closer to the center of circulation of former Tropical Depression 02W and the Japan Meteorological Agency classified the system as Tropical Storm Sanba.  The distribution of storms was asymmetrical.  The stronger thunderstorms were occurring in bands west of the center of circulation.  The bands in the eastern half of the circulation consisted primarily of showers and lower clouds.  Sanba is moving south of a strong upper level ridge.  The ridge is producing easterly winds which are causing moderate vertical wind shear.  The wind shear is causing the asymmetrical distribution of thunderstorms.

Tropical Storm Sanba will move through an environment marginally favorable for intensification.  Sanba will move over water where the Sea Surface Temperature is near 29°C.  So, there is sufficient energy in the upper ocean to support intensification.  However, the upper level ridge will continue to generate moderate vertical wind shear which will inhibit intensification.  Tropical Storm Sanba could get a little stronger during the next 24 to 36 hours.

The ridge is steering Tropical Storm Sanba toward the west and a general westerly motion is expected to continue.  On its anticipated track Tropical Storm Sanba could approach Mindanao in the southern Philippines in about 36 hours.  Sanba could bring gusty winds and locally heavy rain to parts of the southern Philippines.  Locally heavy rain could cause flash floods.

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.

Tropical Depression Tembin Passes Near Southern Tip of Vietnam

The center of Tropical Depression Tembin passed near the southern tip of Vietnam on Monday night.  At 10:00 p.m. EST on Monday the center of Tropical Depression Tembin was located at latitude 8.5°N and longitude 104.6°E which put it about 200 miles (320 km) southwest of Ho Chi Minh City, Vietnam.  Tembin was moving toward the west at 14 m.p.h. (22 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 1005 mb.

An upper level ridge north of Tropical Depression Tembin continued to produce strong easterly winds which were blowing across the top of the circulation.  Those winds were causing strong vertical wind shear.  The shear was strong enough to prevent thunderstorm from developing in most parts of the circulation of Tropical Depression Tembin.  A few thunderstorms formed in the extreme northwestern portion of the circulation, but most of the circulation consisted of bands of low clouds and showers.  The strong shear and lack of tall thunderstorms caused the wind speeds at the surface to decrease and Tembin weakened to a tropical depression.

Tropical Depression Tembin will remain in an environment that is unfavorable for intensification.  Tembin will move over water where the Sea Surface Temperature is near 29°C.  So, there is enough energy in the upper ocean to support intensification.  However, the upper ridge will continue to produce strong easterly winds.  The vertical wind shear is likely to cause the circulation of Tropical Depression Tembin to spin down.

The ridge north of Tembin has been steering the tropical depression toward the west and a general westerly motion is expected to continue for another day or two.  On its anticipated track Tropical Depression Tembin will move across the Gulf of Thailand.   The center of Tropical Depression Tembin could reach the coast of Thailand near Sichon in about 36 hours.