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Typhoon Nepartak Rapidly Intensifies As It Moves Toward Taiwan

Typhoon Nepartak intensified rapidly on Tuesday and it is now the equivalent of a major hurricane.  At 11:00 a.m. EDT on Tuesday the center of Typhoon Nepartak was located at latitude 17.6°N and longitude 132.7°E which put it about 945 miles (1525 km) east-southeast of Taipei, Taiwan.  Nepartak was moving toward west-northwest at 21 m.p.h. (34 km/h).  The maximum sustained wind speed was 140 m.p.h. (225 km/h) and there were wind gusts to 165 m.p.h. (270 km/h).  The minimum surface pressure was 933 mb.

Tyyphoon Nepartak is the equivalent of a Category 4 hurricane on the Saffir-Simpson Scale.  The Hurricane Intensity Index (HII) for Nepartak is 28.3.  The Hurricane Size Index (HSI) is 16.6 and the Hurricane Wind Intensity Size Index (HWISI) is 44.9.  These indices mean that Nepartak is capable of causing regionalized significant damage.

Typhoon Nepartak is very well organized.  It has a well formed eye, which is surround by a ring of strong thunderstorms.  Additional spiral bands of thunderstorms are rotating around the core of the circulation.  Nepartak is generating strong upper level divergence which is pumping out a lot of mass and is allowing the surface pressure to decrease rapidly.

Typhoon Nepartak is in an environment that is favorable for further intensification.  It is moving over water where the Sea Surface Temperature (SST) is near 31°C.  The upper level winds are weak and there is very little vertical wind shear.  Nepartak could intensify into the equivalent of a Category 5 hurricane on the Saffir-Simpson Scale during the next 24 to 36 hours.  If one of the rainbands wraps around the existing eye, then concentric eyewalls could form.  If concentric eyewalls develop, then an ensuing eyewall replacement cycle could cause fluctuations in the intensity of Typhoon Nepartak.

A subtropical ridge northeast of Nepartak is steering the typhoon toward the west-northwest and that general motion is expected to continue for another day or two.  On its anticipated track Typhoon Nepartak could be very near the southernmost islands of Japan and the coast of Taiwan in 36 to 48 hours.  It is likely to be a strong typhoon at that time.  Nepartak could cause significant wind damage.  It could also produce heavy rain that could lead to flash floods and mudslides.

Nepartak Intensifies Into a Typhoon

Tropical Storm Nepartak intensified into a typhoon on Monday as it moved west of Guam.  At 11:00 p.m. EDT on Monday the center of Typhoon Nepartak was located at latitude 15.8°N and longitude 136.0°E which put it about 870 miles (1400 km) southeast of Okinawa.  Nepartak was moving toward the west-northwest at 20 m.p.h. (32 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 974 mb.

The Hurricane Intensity Index (HII) for Typhoon Nepartak was 10.4.  The Hurricane Size Index (HSI) was 3.7 and the Hurricane Wind Intensity Size Index (HWISI) was 14.1.

The structure of Typhoon Nepartak improved on Monday.  A circular area of strong thunderstorms developed at the center of circulation.  Those thunderstorms generated upper level divergence that pumped out mass in all directions, which allowed the surface pressure to decrease.  Several other bands of thunderstorms spiraled around the core of Nepartak.

Typhoon Nepartak is moving over water where the Sea Surface Temperature (SST) is near 31°C.  Nepartak moved into an area where the upper level winds were weaker and the vertical wind shear was reduced.  The combination of very warm water and reduced shear allowed Nepartak to organize and strengthen into a typhoon.  It is expected to remain in an environment favorable for intensification, and Nepartak will grow into a stronger typhoon during the next several days.

A ridge of high pressure northeast of Nepartak is steering the typhoon toward the west-northwest and that general motion is expected to continue for the next several days.  On its anticipated track Typhoon Nepartak could be approaching the southernmost islands of Japan and Taiwan in 48 to 60 hours.  It could be a very strong typhoon at that time.

Tropical Storm Nepartak Develops South of Guam

A center of circulation organized within an area of thunderstorms south of Guam and the system was designated Tropical Storm Nepartak.  At 11:00 p.m. EDT on Sunday the center of Tropical Storm Nepartak was located at latitude 12.2°N and longitude 141.4°E which put it about 215 miles (345 km) west-southwest of Guam.  Nepartak was moving northwest at 16 m.p.h. (26 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.

The circulation of Tropical Storm Nepartak is still organizing.  A primary rainband wrapped around the center and a circular area of thunderstorms formed at the core of the circulation.  The area of thunderstorms is generating upper level divergence which is pumping out mass and allowing the surface pressure to decrease.  Winds to tropical storm force extend our about 100 miles (160 km) from the center of circulation.

An upper level low located north of Nepartak is producing southwesterly winds which area blowing over the top of the tropical storm.  Those winds are creating some vertical wind shear, which is slowing the intensification of Nepartak.  However, the upper low is also enhancing upper level divergence to the northeast of the tropical storm.  Nepartak is moving over water where the Sea Surface Temperature is near 30°C.  The environment is favorable for intensification and Nepartak could become a hurricane during the next several days.

A subtropical ridge located northeast of Nepartak is steering the tropical storm toward the northwest.  That general motion is expected to continue during the next few days.  On its anticipated track, Nepartak could be approaching the southernmost islands of Japan in three or four days.  It is likely to be a typhoon at that time.

Typhoon Koppu Still Affecting Northern Luzon

The center of Typhoon Koppu moved across northern Luzon on Sunday and it is still affecting that region.  At 11:00 p.m. EDT on Sunday the center of Typhoon Koppu was located at latitude 17.5°N and longitude 120.3°E which put it about 200 miles (320 km) north-northwest of Manila, Philippines and just west of the coast of northwestern Luzon.  Koppu was moving toward the north-northeast at 5 m.p.h. (8 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 968 mb.

Passage over northern Luzon weakened Typhoon Koppu and its structure is asymmetrical.  Most of the stronger thunderstorms are located in the western half of the circulation.  Much of the eastern half of the circulation is still over Luzon and there are few thunderstorms there.  The center of circulation is just west of Luzon.  Since it is back over water, the core of the typhoon could start to reorganize.  Intensification will be limited because of the large proportion of the circulation which is over land.

Koppu is near the western end of a subtropical ridge, which is causing the typhoon to move slowly northward.  That motion could continue for another 24 to 36 hours.  Eventually the ridge is expected to strengthen and push Typhoon Koppu northward at a faster speed.  Typhoon Koppu will continue to bring heavy rain to parts of northern Luzon for another day or two.

Dangerous Typhoon Koppu Making Landfall in Northern Luzon

Typhoon Koppu intensified rapidly during the past 12 hours and it is making landfall near Baler in northern Luzon as the equivalent of a Category 4 hurricane on the Saffir-Simpson Scale.  At 11:00 a.m. EDT on Saturday the center of Typhoon Koppu was located at latitude 16.0°N and longitude 122.9°E which put it about 170 miles (275 km) east-northeast of Manila, Philippines.  Koppu was moving toward the west-northwest at 7 m.p.h. (11 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 918 mb.  Typhoon Koppu has a Hurricane Intensity Index (HII) of 31.6, a Hurricane Size Index (HSI) of 17.5 and a Hurricane Wind Intensity Size Index (HWISI) of 49.1, which means it is capable of producing regional significant wind damage.  In addition the slow movement of Koppu means it will produce very heavy rainfall which will create the potential for serious flooding and landslides.

Koppu will continue to move toward the west-northwest for another 12 to 24 hours.  Then it will reach the western end of the subtropical ridge that has been steering it and start to move toward the north.  Although Typhoon Koppu will weaken as it moves across northern Luzon, it will be over that area for 36 to 48 hours.  Koppu has the potential to cause widespread damage due to winds, floods and landslides.

Typhoon Koppu Continues to Intensify and Threaten Luzon

Typhoon Koppu continued to intensify on Friday and it maintained its steady course toward northern Luzon.  At 5:00 p.m. EDT on Friday the center of Typhoon Koppu was located at latitude 15.8°N and longitude 124.5°E which put it about 270 miles (435 km) east-northeast of Manila, Philippines.  Koppu was moving toward the west at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 110 m.p.h. (175 km/h) and there were wind gusts to 130 m.p.h. (210 km/h).  The minimum surface pressure was 947 mb.

Typhoon Koppu is evolving into a large well organized typhoon.  An eye has formed at the center of the circulation and multiple rain bands spiral around the core of the typhoon.  Upper level divergence is pumping mass away from the center of circulation.  Koppu is moving over water where the Sea Surface Temperature is near 30°C.  The upper level winds are light and there is not much vertical wind shear.  Koppu is likely to continue to intensify until it begins to interact with northern Luzon.

A subtropical ridge is steering Koppu toward the west and that steering pattern is expected to continue for another 24 to 36 hours.  On its anticipated track the center of Typhoon Koppu will be very near the northeastern coast of Luzon in about 24 hours.  Koppu will bring strong winds, heavy rain and a storm surge to northern Luzon.  The large size of Koppu and its relatively slow movement means that it could produce very heavy rainfall.  Serious flooding and numerous mudslides are possible across northern Luzon.

Intensifying Typhoon Koppu Moving Toward Northern Luzon

Typhoon Koppu intensified on Thursday as it continued to move steadily toward Northern Luzon.  At 11:00 p.m. EDT the center of Typhoon Koppu was located at latitude 15.6°N and longitude 126.9°E which put it about 425 miles (685 km) east of Manila, Philippines.  Koppu was moving toward the west at 8 m.p.h. (13 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 969 mb.

Typhoon Koppu is moving over water where the Sea Surface Temperature is near 30°C.  The upper level winds lessened on Thursday which decreased the vertical wind shear and allowed Koppu to intensify more quickly.  The core of the circulation consolidated and there are suggestions that an eyewall may be forming.  Koppu is expected to move through a favorable environment until it reaches northern Luzon and further intensification is very likely.

A subtropical ridge is steering Koppu toward the west and that general steering pattern is expected to continue for another 36 to 48 hours.  On its anticipated track, Typhoon Koppu will approach northern Luzon in 36 to 42 hours.  It could bring strong winds, heavy rain and a storm surge when it reaches that area.  The heavy rain could produce floods and mudslides as Koppu moves over northern Luzon.

Tropical Storm Koppu Forms North of Yap

In spite of significant vertical wind shear a surface circulation has been consolidating inside an area of thunderstorms north of Yap.  The system has been designated Tropical Storm Koppu.  At 5:00 p.m. EDT on Tuesday the center of Tropical Storm Koppu was located at latitude 15.7°N and longitude 137.1°E which put it about 430 miles (690 km) north of Yap.  Koppu was moving toward the west at 14 m.p.h. (23 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 993 mb.

Significant vertical wind shear is inhibiting the organization of Tropical Storm Koppu.  An upper level ridge north of Koppu is generating strong northeasterly winds over the top of the tropical storm.  The vertical wind shear is causing most of the strong thunderstorms to be located southwest of the center of circulation.  The only other deep convection is occurring in a band that is west of the core of the circulation.

Koppu is over water where the Sea Surface Temperature is near 30°C and so there is plenty of energy in the upper ocean.  The wind shear will inhibit intensification for another 24 to 48 hours before it starts to subside.  Koppu could intensify much more quickly later this week when it moves into an area where the upper level winds are lighter.  Koppu could become a typhoon withing 36 to 48 hours and it could be a strong typhoon by the end of the week.

A subtropical ridge is steering Tropical Storm Koppu quickly to the west.  That general motion is expected to continue for the rest of the week.  On its anticipated track Koppu could be approaching northern Luzon in about three or four days.  It could be a significant typhoon by that time.

Typhoon Mujigae Making Landfall in China

Strong Typhoon Mujigae is making landfall on the coast of China near Zhanjiang.  At 11:00 p.m. EDT on Saturday the center of Typhoon Jiang was located at latitude 20.8°N and longitude 111.1°E which put it about 55 miles (90 km) southeast of Zhanjiang.  Mujigae was moving toward the northwest at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 110 m.p.h. (175 km/h) and there were wind gusts to 130 m.p.h. (215 km/h).  The minimum surface pressure was 949 mb.

The northwestern side of the eyewall is beginning to affect the coast of China.  Mujigae will bring strong winds and heavy rain as it moves inland over southern China.  The typhoon will begin to weaken as soon as the center moves over land and it will gradually spin down over southern China.

Tropical Storms Mujigae and Choi-Wan Form Over NW Pacific

Two new tropical storms with the names of Mujigae and Choi-Wan have formed over the western North Pacific Ocean.  At 11:00 a.m. EDT on Friday the center of Tropical Storm Mujigae was located at latitude 17.4°N and longitude 117.3°E which put it about 275 miles (445 km) northwest of Manila, Philippines.  Mujigae was moving toward the west-northwest at 17 m.p.h.  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 990 mb.

At 11:00 a.m. EDT on Friday the center of Tropical Storm Choi-Wan was located at latitude 19.2°N and longitude 166.4°E which put it about 15 miles (20 km) south-southeast of Wake Island.  Choi-Wan was moving toward the west-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 50 m.p.h. (80 km/h).  The minimum surface pressure was 996 mb.

Tropical Storm Mujigae organized quickly after the system move west of the Philippines.  A primary curved rainband wrapped around the western and southern sides of the center of circulation.  A possible eye is apparent intermittently on infrared satellite imagery.  Upper level divergence is beginning to occur both north and south of the center.  Mujigae is moving over water where the Sea Surface Temperature is near 28°C and there is not enough vertical wind shear to prevent intensification.  A period of rapid intensification is possible and Mujigae could become a typhoon in 12 to 24 hours.

A subtropical ridge is steering Mujigae toward the west-northwest and that general motion is expected to continue for the next several days.  On its anticipated track, Mujigae could be approaching the southern coast of China in 36 hours.  It could bring strong winds and heavy rain when it makes landfall.

Tropical Storm Choi-Wan is still in the organizational stage.  It has a large broad circulation without a well developed inner core.  Winds to tropical storm force are occurring in clusters of thunderstorms.  Choi-Wan is over Sea Surface Temperatures near 29°C, but there is moderate vertical wind shear over the northern part of the tropical storm.  The wind shear is expected to decrease in a day or two and Choi-Wan is forecast to become a typhoon.

Choi-Wan is between two subtropical ridges and the steering currents are relatively weak.  In a day or two the western ridge is expected to steer Choi-Wan toward the northwest.  Choi-Wan will cause squally weather on Wake Island for 24 to 48 hours.