Category Archives: Western North Pacific

Western Pacific Typhoons and Tropical Storms

Tropical Storm Linfa Nearing Northern Luzon

Tropical Storm Linfa is moving steadily toward the coast of northern Luzon.  At 11:00 p.m. EDT on Friday the center of Tropical Storm Linfa was located at latitude 16.1°N and longitude 123.9°E which put it about 230 miles (370 km) east-northeast of Manila, Philippines.  Linfa was moving toward the northwest at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 989 mb.

Tropical Storm Linfa has a small circulation, but it appears to be intensifying quickly.  A circular area of strong thunderstorms has developed around the center of circulation and it is producing strong upper level outflow.  Linfa is over water where the Sea Surface Temperature is near 30°C.  An upper level ridge northwest of the tropical storm is producing some vertical wind shear, but the shear does not seem to be enough to prevent intensification.  Linfa has about 18 hours to intensify before it reaches the coast of Luzon and it could attain typhoon intensity before it gets there.  Mountains in northern Luzon will disrupt the lowers levels of the circulation and Linfa will weaken after if makes landfall.

A subtropical ridge is steering Linfa toward the northwest and that steering pattern is expected to continue until the tropical storm makes landfall in northern Luzon.   Linfa will reach the western end of the subtropical ridge while it is over Luzon and if the circulation remains intact vertically, it will turn toward the north.  On its anticipated track Linfa will make landfall in northern Luzon in about 18 hours.  It is expected to eventually turn north toward Taiwan and the southern islands of Japan.  Linfa cold bring strong winds and locally heavy rainfall for parts of northern Luzon.  Heavy rainfall could contribute to flooding and mudslides in some locations.

Tropical Storm Chan-hom Moving Toward Marianas

Tropical Storm Chan-hom has resumed a northwesterly motion and it is moving toward the Mariana Islands.  At 11:00 p.m. EDT on Friday the center of Tropical Storm Chan-hom was located at latitude 12.7°N and longitude 148.2°E which put it about 250 miles (400 km) east-southeast of Guam.  Chan-hom was moving toward the northwest at 11 m.p.h. (18 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 989 mb.  A Typhoon Watch is in effect for Guam, Rota, Tinian and Saipan.

The upper level low that produced the vertical wind shear which blew the top off Chan-hom on Thursday moved northeast and the upper level winds decreased on Friday.  A reduction in vertical wind shear allowed new thunderstorms to develop around the center of circulation and the circulation became better organized.  The thunderstorms near the center are beginning to generate upper level divergence and more spiral bands appear to be forming.  Chan-hom is over water where the Sea Surface Temperature is near 29°C.  The environment is favorable for intensification and rapid intensification is possible, if the wind shear remains modest.  Chan-hom could attain typhoon intensity before it reaches the Mariana Islands.

A subtropical ridge is steering Chan-hom toward the northwest and that ridge is expected to continue to steer it in the same general direction during the next few days.  On its anticipated track, Chan-hom could approach the Mariana Islands in about 24 hours.  The center could pass north of Guam, but it may pass near to Rota, Tinian or Saipan.  Chan-hom will bring wind and heavy rain to any islands it crosses.

Tropical Storm Nangka Forms East of Kwajalein

Another tropical storm formed over the western North Pacific when a circulation developed west of the International Dateline and was designated as Tropical Storm Nangka (11W).  At 11:00 p.m. EDT on Friday the center of Tropical Storm Nangka was located at latitude 9.9°N and longitude 169.2°E which put it about 150 miles east-northeast of Kwajalein.  Nangka was moving toward the west-northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 992 mb.

Tropical Storm Nangka is moving over water where the Sea Surface Temperature is near 30°C.  The upper level winds are light and upper level divergence is increasing.  However, there is sinking drier air north of the tropical storm and the circulation appears to be pulling some of the drier air into it.  As a result many of the stronger thunderstorms are occurring in the western half of the circulation.  The drier air could inhibit intensification in the short term.  The other favorable environmental factors are likely to produce intensification in the longer term once Nangka moves west of the drier air.

A subtropical ridge north of Nangka is expected to steer it in a west-northwesterly direction during the next few days.  On its expected track Nangka will bring wind and rain to a number of atolls in the Marshall Islands.  Nangka could approach the Mariana Islands in a few days.

Wind Shear Affecting Tropical Storm Chan-hom

Although Tropical Storm Chan-hom briefly reached typhoon intensity on Thursday, strong upper vertical wind shear quickly weakened it back to a tropical storm.  At 11:00 p.m. EDT on Thursday the center of Tropical Storm Chan-hom was located at latitude 10.3°N and longitude 148.0°E which put it about 325 miles (525 km) southeast of Guam.  Chan-hom was moving toward the west at 6 m.p.h. (10 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 981 mb.  A Typhoon Watch has been issued for Guam, Rota, Tinian and Saipan.

The combination of a upper level ridge and an upper level low produced strong northeasterly winds that blew the middle and upper portions of the circulation of Chan-hom west of the low level circulation.  The middle and upper parts of the circulation are about 100 miles (160 km) southwest of the surface center.  There are no thunderstorms currently near the surface center.  The upper level winds and the vertical wind shear they are producing are likely to continue to weaken Chan-hom on Friday.  The upper low is expected to move eastward during the next several days, which would result in a decrease in the wind shear.  If the surface circulation is still intact, it will be over warm Sea Surface Temperatures and reintensification would be possible.

Chan-hom is likely to be steered toward the west on Friday by the winds in the lower levels.  If new thunderstorms develop near the center and the height of the circulation increases, then a subtropical ridge in the middle levels could cause the tropical storm to turn toward the northwest.  If that turn occurs on Friday, it could put Chan-hom on a track toward Guam, Saipan or Tiniana.  If the turn occurs later in the weekend, then Chan-hom could pass to the south of those islands before it turns toward the northwest.

Tropical Storm Linfa Forms East of the Philippines

A well defined low level circulation developed in an area of thunderstorms east of the Philippines on Thursday and the system was designated as Tropical Storm Linfa (10W).  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Linfa was located at latitude 16.3°N and longitude 127.6°E which put it about 470 miles (760 km) east-northeast of Manila, Philippines.  Linfa was moving toward the northwest at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 993 mb.

Linfa developed over water where the Sea Surface Temperature (SST) is near 30°C,  There is sufficient energy in the upper ocean to support intensification.  An upper level ridge centered northwest of Linfa is producing northeasterly winds over the top of the circulation and most of the thunderstorms are occurring west of the center.  The vertical wind shear is modest and some upper level divergence is present, especially over the western half of the circulation.  The vertical wind shear is expected to remain moderate and Linfa could intensify during the next several days.  If the upper level winds weaken, then a period of more rapid intensification is possible.

Linfa is being steered by a subtropical ridge located to the east of the tropical storm.  The ridge is expected to steer it toward the northwest in the short term.  As Linfa reaches the western end of the ridge it is expected to be steered more toward the north.  The timing of the turn toward the north will be important because it will determine if Linfa moves over the northern Philippines or moves northeast of that area.  The timing on the turn to the north will also determine the potential risk for Taiwan.  Another factor that could complicated the track forecast is a potential interaction with Typhoon Chan-hom which is abut 1500 miles (2400 km) east-southeast of Linfa.

Tropical Storm Chan-hom Forms East of Guam

A center of circulation developed in an area of thunderstorms on the opposite side of the Equator from Tropical Cyclone Raquel and it was designated as Tropical Storm Chan-hom on Tuesday.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Chan-hom was located at latitude 11.0°N and longitude 156.5°E which put it about 250 miles (400 km) north-northeast of Oroluk atoll and about 800 miles (1290 km) east of Guam.  Chan-hom was moving toward the west at 22 m.p.h. (35 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 993 mb.

Tropical Storm Chan-hom formed over water where the Sea Surface Temperatures (SSTs) are around 29°C to 30°C and there is plenty of energy in the upper ocean to support intensification.  An upper level ridge located north of the tropical storm is generating easterly winds over the top of the circulation.  The easterly winds are generating moderate amounts of vertical wind shear and many of the stronger thunderstorms are occurring in the western half of the circulation.  Those thunderstorms are producing strong rising motion and upper level divergence is well developed on the western side of Chan-hom.  However the upper level easterly winds are interfering with upper level divergence on the eastern side of the tropical storm.  As a result, a modest rate of intensification is expected in the short term.  If the upper level winds were to lessen, then a more rapid rate of intensification would be possible.

The upper level ridge is expected to steer Chan-hom toward the west during the next several days.  On its anticipated track Chan-hom could approach Guam in about three days.  It could be a typhoon by that time.  However, there is some divergence in the track guidance from numerical models at the end of this week and that is producing uncertainty about the future track of Chan during that time period.

Tropical Storm Kujira Makes Landfall on Hainan Island

Tropical Storm Kujira made landfall on the east coast of Hainan Island on Monday.  At 11:00 p.m. EDT on Monday the center of Tropical Storm Kujira was located at latitude 19.9°N and longitude 109.1°E which put it about 100 miles (160 km) south of Beihai, China.  Kujira was moving toward the northwest 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 992 mb.

Passing across Hainan Island weakened Tropical Storm Kujira on Monday.  In addition, an upper level ridge over southern Asia continues to generate vertical wind shear over the tropical storm.  However, it will move over warm water when the center moves northwest of Hainan Island.  So, Kujira could maintain tropical storm intensity until it makes another landfall in China in about 18 to 24 hours.  The primary risk will be locally heavy rainfall.

Tropical Storm Kujira Nearing Hainan Island

Tropical Storm Kujira moved slowly northward on Sunday.  At 11:00 p.m. EDT on Sunday night the center of Tropical Storm Kujira was located at latitude 18.0°N and longitude 111.2°E which put it about 150 miles (240 km) south-southeast of Xuwen, China.  Kujira was moving toward the north-northwest at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 994 mb.

Although Kujira is moving over water where the Sea Surface Temperature is near 30°C, vertical wind shear is inhibiting intensification.  An upper level ridge over southern Asia is producing northeasterly winds over the top of Kujira.  As a result of the vertical shear, most of the stronger thunderstorms are occurring southwest of the center of circulation.  As Kujira moves farther north, some of the circulation will move over Hainan Island, which will further limit the potential for intensification.

Kujira is moving around the western end of a subtropical ridge which is steering the tropical storm toward the north.  The steering pattern is expected to remain in place for the early part of the week.  Kujira could be very close to the east coast of Hainan Island in about 12 hours.  It will move near or just east of Hainan and Kujira could make landfall in China in 24 to 36 hours.  Although it will bring some wind, the primary risk will be locally heavy rainfall.

Tropical Storm Kujira Forms South of Hainan Island

A surface circulation organized within a larger area of thunderstorms east of Vietnam on Saturday and the system was designated as Tropical Storm Kujira.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Kujira was located at latitude 15.7°N and longitude 111.4°E which put it about 210 miles (340 km) east of Da Nang, Vietnam.  Kujira was moving north-northwest at 3 m.p.h. (5 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 998 mb.

Tropical Storm Kujira is moving over water where the Sea Surface Temperature is near 30°C.  However an upper level ridge over southern Asia is generating northeasterly winds over the top of Kujira.  Those northeasterly winds are producing moderate vertical wind shear, which is causing most of the stronger thunderstorms to be located in the western half of the circulation.  Some spiral bands are beginning to form and a band is wrapping around the southern side of the center of circulation.  It appears that Kujira is becoming more well organized and intensification is likely, although the wind shear could slow that process.

Kujira is in an area where the steering currents are weak.  The tropical storm is near the western end of a subtropical ridge and the highest probability is that it will move north toward Hainan Island and southern China.  Some numerical models project a landfall on Hainan Island, but others have Kujira passing east of the island before making landfall on the coast of China.  In either scenario Kujira could approach Hainan Island in 24 to 36 hours.

Typhoon Dolphin Is Bringing Wind and Heavy Rain to Iwo To

Even though the center of Typhoon Dolphin is still over 100 miles from Iwo To, it is bringing wind and heavy rain to that island.  The most recent surface observation reported southeast winds at 43 m.p.h. with gusts to 66 m.p.h.  At 11:00 p.m. EDT on Monday the center of Typhoon Dolphin was located near latitude 24.6° and longitude 139.7°E which put it about 140 miles west-southwest of Iwo To.  Dolphin was moving toward the northeast at 10 m.p.h.  The maximum sustained wind speed was 85 m.p.h. and there were gusts to 105 m.p.h.  The minimum surface pressure was 967 mb.

Dolphin will continue to move over cooler Sea Surface Temperatures as it moves farther north.  It will also encounter strong upper level westerly winds, which will increase vertical wind shear.  So, Typhoon Dolphin will weaken steadily on Tuesday.  It will eventually transition into an extratropical cyclone as it passes southeast of Japan.

Upper level westerly winds are steering Typhoon Dolphin toward the northeast.  It is expected to accelerate toward the northeast on Tuesday.  On its anticipated track the center of Dolphin will pass northwest of Iwo To during the next few hours.  It could pass very near Chichi Jima on Tuesday and bring strong wind and heavy rain.