Category Archives: Western North Pacific

Western Pacific Typhoons and Tropical Storms

Typhoon Mindulle Nearing Japan

Typhoon Mindulle moved steadily toward the coast of Japan on Sunday.  At 2:00 p.m. EDT on Sunday the center of Typhoon Mindulle was located at latitude 32.9°N and longitude 139.4°E which put it about 185 miles (305 km) south of Tokyo, Japan.  Mindulle was moving toward the north at 19 m.p.h. (31 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 975 mb.

The circulation of Typhoon is reasonably well organized.  A primary rainband wraps most of the way around the northern and eastern sides of the center of circulation.  There is evidence of a partial eyewall north of the center.  Additional bands of thunderstorms are occurring in the northern half of the circulation.  The thunderstorms near the core of Mindulle are generating upper level divergence which is pumping away mass to the east of the typhoon.  However, there are fewer thunderstorms west of the center of circulation which may indicate the presence of dry air in that area.

Typhoon Mindulle is moving through an environment that is only marginal for further intensification.  It is currently moving over water where the Sea Surface Temperature is near 29°C, but Mindulle will move over cooler water when it approaches the coast of Japan.  An upper level trough located to the west of Japan is generating southwesterly winds which are blowing across the top of Mindulle.  The moderate vertical wind shear is preventing upper level divergence to the west of the typhoon and the shear may also be partially responsible for the asymmetric distribution of thunderstorms.  It is also possible that Mindulle is pulling in some drier air located northwest of the typhoon.

The upper level trough is steering Mindulle toward the north and that general motion is expected to continue.  On its anticipated track the center of Typhoon Mindulle will reach the coast near Tokyo in 10-12 hours.  Heavy rain in some of the bands of thunderstorms north of the center could reach the coast at any time.  Since Mindulle is a typhoon, it is capable of causing minor wind damage.  A greater risk is the potential for locally heavy rainfall and flash flooding.

Tropical Storms Lionrock and Kompasu Spin Up Near Japan

A large cyclonic atmospheric gyre near Japan spun up two more tropical storms at the end of the week.  The Japan Meteorological Agency named two smaller circulations within the larger gyre Tropical Storm Lionrock and Tropical Storm Kompasu.

At 2:00 p.m. EDT on Saturday the center of Tropical Storm Kompasu was located at latitude 37.8°N and longitude 142.3°E which put it about 75 miles (120 km) east of Sendai, Japan.  Kompasu was moving toward the northwest at 26 m.p.h. (42 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.

At 2:00 p.m. EDT on Saturday the center of Tropical Storm Lionrock was located at latitude 30.6°N and longitude 135.7°E which put it about 530 miles (860 km) east-northeast of Okinawa.  Lionrock was moving toward the west-southwest at 8 m.p.h. (13 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 994 mb.

Tropical Storm Kompasu is located farther north and it is beginning to make a transition into an extratropical cyclone.  Kompasu is moving over water where the Sea Surface Temperature (SST) is near 26°C, but it is moving rapidly toward cooler SSTs.  Most of the thunderstorms are in a single primary rainband that wraps around the southern part of the circulation.  An upper level trough west of Japan is pulling southwesterly winds across the top of Tropical Storm Kompasu and the vertical wind shear is increasing.

The upper level trough is expected to turn Tropical Storm Kompasu toward the northeast.  On its anticipated track Tropical Storm Kompasu will move across Hokkaido in about 18 hours.  It will bring locally heavy rain and some wind.

Tropical Storm Lionrock is more well organized.  Several spiral bands of thunderstorms are wrapping around the southern and east sides of the center of circulation.  There is drier air in the western portion of the circulation and there are few thunderstorms in that part of Lionrock.  The thunderstorms east of the center are generating upper level divergence that is pumping mass toward the northeast away from core of Tropical Storm Lionrock.

Tropical Storm Lionrock is in an environment that is somewhat favorable for additional intensification.  It is moving over water where the SST is near 30°C.  The upper level trough west of Japan is generating some vertical wind shear.  The drier air in the western part of the circulation will also inhibit intensification, but Lionrock could gradually get better organized.  Upper level outflow from stronger Tropical Storm Mindulle, which is southwest of Lionrock, could produce enough vertical wind shear to weaken Lionrock at times.

The large atmospheric gyre is steering Tropical Storm Lionrock toward the west-southwest.  Lionrock could be pulled more toward the south as the larger, stronger Tropical Storm Mindulle passes east of it.  Tropical Storm Lionrock is expected to remain south of Japan during the next several days.  An alternative scenario would be for Tropical Storm Mindulle to intensify into a typhoon and grow large enough to absorb the circulation of Lionrock.

Tropical Storm Mindulle Forms Northwest of Guam

A smaller center of circulation consolidated within a much larger cyclonic gyre that extends from the Marianas north to Japan and west to China and the system has been designated Tropical Storm Mindulle.  At 11:00 a.m. EDT on Friday the center of Tropical Storm Mindulle was located at latitude 19.5°N and longitude 141.0°E which put it about 410 miles (655 km) south of Iwo To.  Mindule was moving toward the north-northwest at 11 m.p.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 992 mb.

The circulation around Tropical Storm Mindulle is still organizing.  A primary rainband is wrapping about three quarters of the way around the broad center of circulation.  There are few thunderstorms close to the core of tropical storm.  Scattered thunderstorms are forming in broken bands outside the primary rainband.  The thunderstorms in the primary rainband are generating some upper level divergence which is mainly pumping mass to the southwest of the center of circulation.

Tropical Storm Mindulle is in an environment that is favorable for slow intensification.  It is moving over water where the Sea Surface Temperature is near 31°C.  The upper level pattern near Mindulle is quite complex with a number of different features.  A narrow upper level ridge is just north of Mindulle and it is producing northeasterly winds that are blowing across the top of the tropical storm.  The northeasterly winds are contributing to the fact that most of the thunderstorms are west of the center of circulation and they are causing moderate vertical wind shear.  The vertical wind shear is inhibiting intensification.  Tropical Storm Mindulle is expected to extract enough energy from the ocean to intensify.  However, intensification will be slow while the core of the circulation organizes.

Tropical Storm Mindule is moving around the eastern portion of the large cyclonic gyre mentioned above.  That gyre is steering Mindulle toward the north-northwest and a general motion toward the north is expected to continue.  On its anticipated track Tropical Storm Mindulle could pass near Iwo To in about 24 hours.  Mindulle could be near Tokyo, Japan in about three days.

Tropical Storm Dianmu Forms Near Hainan Island

A center of circulation developed within a larger cyclonic rotation associated with the monsoon near Hainan Island and the Japan Meteorological Agency classified the system as Tropical Storm Dianmu.  At 5:00 a.m. EDT on Thursday the center of Tropical Storm Dianmu was located at latitude 20.5°N and longitude 109.7°E which put it about 265 miles (430 km) east of Hanoi, Vietnam.  Dianmu was moving toward the west 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 985 mb.

The circulation of Tropical Storm Dianmu consists of a smaller counterclockwise rotation inside a much larger cyclonic flow associated with the monsoonal circulation.  Thunderstorms clustered around the western and southern portion of the smaller counterclockwise rotation and a distinct inner core developed that is separate from the broader center of the monsoonal gyre.  Additional spiral bands formed outside the core.  The thunderstorms are generating upper level divergence, primarily to the south and west of Tropical Storm Diamnu.

Tropical Storm Dianmu is moving through an environment that is favorable for additional strengthening.  It is moving over water where the Sea Surface Temperature is near 31°C.  An upper level ridge centered over China is producing easterly winds which are blowing across the top of Tropical Storm Dianmu.  Those winds are causing moderate vertical wind shear, which is slowing the rate of intensification of the tropical storm.  The proximity of Dianmu to the coast is also slowing the rate of intensification.  Tropical Storm Dianmu has 12 to 18 hours to intensify before it moves over land.

The upper level ridge over China is steering Tropical Storm Dianmu toward the west and that general motion is expected to continue.  On its anticipated track the center of Tropical Storm Dianmu could reach the coast of Vietnam in 12 to 18 hours.  Dianmu could cause some minimal wind damage and storm surge, but heavy rain will be the greatest threat.  Tropical Storm Dianmu could cause flash flooding when it moves inland over Southeast Asia.

Tropical Storm Chanthu Passes East of Tokyo

Tropical Storm Chanthu brought wind and rain to the east coast of Honshu as the center passed east of Tokyo on Tuesday.  At 5:00 p.m. EDT on Tuesday the center of Tropical Storm Chanthu was located at latitude 37.4°N and longitude 141.6°E which put it about 105 miles (170 km) northeast of Tokyo, Japan.  Chanthu was moving toward the north-northeast at 12 m.p.h. (19 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 995 mb.

Tropical Storm Chanthu is starting the transition from a tropical cyclone to an extratropical cyclone.  It is still moving over water where the Sea Surface Temperature (SST) is near 26°C, but Chanthu will move over colder water during the next 24 hours.  An upper level trough west of Japan will sweep northwesterly winds over the top of Tropical Storm Chanthu.  The increased vertical wind shear will tilt the circulation of Chanthu toward the northeast.  The trough also contains cooler air.  A combination of cooler SSTs, more vertical wind shear and cooler air aloft will alter the structure of Chanthu and it will begin to look more like an extratropical cyclone on Wednesday.

The upper level trough will steer Chanthu in a generally north-northeasterly direction during the next 24 hours.  On its anticipated track Tropical Storm Chanthu will move roughly parallel to the coast of Honshu.  Chanthu is expected to move across Hokkaido later on Wednesday.

The rainbands in Tropical Storm Chanthu are capable of producing locally heavy rainfall.  Some flooding is possible in eastern Honshu and Hokkaido.  Wind damage should be minimal although fishing boats and other vessels along the northeast coast of Japan will have to deal with wind and waves.

Tropical Storm Chanthu Forms South of Japan

A center of circulation consolidated near a cluster of thunderstorms south of Japan on Saturday and the system was designated as Tropical Storm Chanthu.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Chanthu was located at latitude 21.2°N and longitude 143.1°E which put it about 295 miles (475 km) south-southeast of Iwo To.  Chanthu was moving toward the northeast at 14 m.p.h. (23 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.

Although a distinct center of circulation exists in the lower levels of Tropical Storm Chanthu, the storm is not well organized.  Southwesterly winds in the upper levels are causing vertical wind shear which is tilting the upper portion of the circulation toward the northeast.  Most of the thunderstorms associated with Tropical Storm Chanthu are occurring in the northeastern quadrant of the circulation.  Several broken rainbands extend into the southern portion of the circulation, but there are few thunderstorms in the western half of Chanthu.

Tropical Storm Chanthu is moving through an environment that is marginally favorable for intensification.  Chanthu is moving over water where the Sea Surface Temperature is near 30°C.  However, an upper level trough west of Chanthu is causing the southwesterly winds which are blowing across the top of the tropical storm.  Moderate vertical wind shear will inhibit intensification in the short term.  As Tropical Storm Chanthu moves farther north, it could move into a region where the upper level winds are not as strong.  If the vertical wind shear decreases, then Chanthu could intensify.

Winds from the upper level trough are steering Tropical Storm Chanthu toward the northeast.  As the tropical storm moves farther north, a subtropical ridge located east of Chanthu will steer it more toward the north.  On its anticipated track, the center of Tropical Storm Chanthu is expected to pass east of Iwo To in about 24 hours.  Tropical Storm Chanthu could be approaching the coast of Japan near Tokyo in about three or four days.

Tropical Storm Omais Forms over the Northern Marianas

A very broad area of low pressure developed enough of the characteristics of a tropical cyclone to be classified as Tropical Storm Omais on Thursday.  At 11:00 p.m. EDT on Thursday the center of Tropical Storm Omais was located at latitude 19.5°N and longitude 146.2°E which put it about 380 miles (615 km) north-northeast of Guam.  Omais was moving toward the north 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.

The circulation of Tropical Storm Omais is not well organized.  Several clusters of thunderstorms exist about 100 miles (160 km) east and south of the center of the very broad low pressure system.  No thunderstorms are occurring in the western half of the low or near the center of the circulation.  An inner core does not exist at this time and the strongest winds are occurring in the clusters of thunderstorms well removed from the center.

Tropical Storm Omais is in an environment that is favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 30°C.  The upper level environment is also somewhat favorable for intensification.  An upper level low is northwest of Omais and an upper level ridge is east of the tropical storm.  Those two features are generating southwesterly winds which are blowing over the top of Tropical Storm Omais.  The vertical wind shear is inhibiting the organization and intensification of Omais.

The environment should allow Tropical Storm Omais to intensify, but the large circulation will reduce the rate of intensification.  As the wind field contracts and the strongest winds move closer to the center of circulation, the structure of Tropical Storm Omais will move closely resemble a typical tropical cyclone.  When an inner core forms at the center of circulation, the rate of intensification may increase.

Tropical Storm Omais is near the western end of a subtropical ridge.  The steering currents are weak, but Omais is likely to move slowly toward the north in the short term.  A faster motion is expected over the weekend.  On its anticipated track Tropical Storm Omais will move near the northernmost Marianas and pass east of Iwo To.

Typhoon Nida Makes Landfall Near Hong Kong

Typhoon Nida made landfall on Monday near Hong Kong on the coast of China.  At 5:00 p.m. EDT on Monday the center of Typhoon Nida was located at latitude 22.8°N and longitude 114.4°E which put it about 50 miles (80 km) east-northeast of Hong Kong.  Nida was moving toward the northwest t 13 m.p.h.  The maximum sustained wind speed was 95 m.p.h. (155 km/h) and there were wind gusts to 115 m.p.h. (185 km/h).  The minimum surface pressure was 963 mb.

Typhoon Nida made landfall on the southeast coast of China just to the north of Hong Kong.  The core of Nida is large and the typhoon is capable of causing wind damage on a regional scale.  Wind blowing toward the coast could also generate a storm surge until Typhoon Nida moves farther inland.  However, very heavy rain and fresh water flooding are much greater risks as Nida moves farther inland over China.

A subtropical ridge north of Nida is steering the typhoon toward the northwest and that general motion is expected to continue for the next several days.  The ridge will steer Nida farther inland over southeastern China.  Typhoon Nida’s fairly slow motion and large size mean that heavy rain could fall over an expansive area.  The risk for flooding will continue as Nida moves inland.

Typhoon Nida Brushes Luzon and Heads for Hong Kong

Typhoon Nida brought wind and rain to northern Luzon on Sunday as it continued to move toward Hong Kong on the coast of China.  At 11:00 p.m. EDT on Sunday the center of Typhoon Nida was located at latitude 20.4°N and longitude 118.3°E which put it about 340 miles (545 km) east-southeast of Hong Kong.  Nida was moving toward the west-northwest at 17 m.p.h. (27 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 Nida is 10.4.  The Hurricane Size Index (HSI) is 13.1 and the Hurricane Wind Intensity Size Index (HWISI) is 23.5.  These indices suggest that Typhoon Nida will be capable of causing minor wind damage on a regional scale.

The structure of Typhoon Nida changed significantly on Sunday.  The primary rainband wrapped around the core of the circulation and a very large eye was created at the center.  The diameter of the eye is approximately 50 miles (80 km).  The strongest winds are occurring in the ring of thunderstorms that surrounds the eye.  Other spiral bands of thunderstorms are rotating around the large eye.  The thunderstorms were generating upper level divergence which pumped out mass and allowed the surface pressure to decrease.

Typhoon Nida is in an environment that would favor intensification.  It is moving over water where the Sea Surface Temperature is near 30°C.  Easterly winds are blowing in the upper levels, but there is not much vertical wind shear.  The large size of the eye of Nida is the major factor inhibiting intensification.  It takes more energy to increase the wind speed in a large typhoon than it does in a smaller storm.  If the eye contracts, then Typhoon Nida could intensify more before it makes landfall.

A subtropical ridge north of Nida is steering the typhoon toward the west-northwest and that general motion is expected to continue for another day or so.  On its anticipated track Typhoon Nida will be very near Hong Kong in about 24 hours.

As mentioned above, the large size of Typhoon Nida means that it will be capable of causing wind damage on a regional scale.  In addition, Typhoon Nida will be capable of creating a significant storm surge when it moves into the coast of China.  A large slow moving typhoon like Nida will also produce heavy rain and flooding as it moves inland.

Intensifying Tropical Storm Nida Nears Northern Philippines

Tropical Storm Nida intensified on Saturday as it slowly approached the northern portion of Luzon in the Philippines.  At 5:00 p.m. EDT (2100 UTC) the center of of Tropical Storm Nida was located at latitude 16.5°N and longitude 123.8°E which put it about 245 miles (395 km) east-northeast of Manila, Philippines.  Nida was moving toward the west-northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 50 m.p.h. (95 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 Nida has become increasingly well organized during the past 24 hours.  A primary rainband wraps about two thirds of the way around the western and southern sides of the center of circulation.  Additional spiral bands of thunderstorms are developing outside the core of the circulation.  Rising motion associated with the convection is generating upper level divergence which is pumping out mass and allowing the surface pressure to decrease.

Tropical Storm Nida is moving through an environment that is very favorable for further intensification.  It is moving over water where the Sea Surface Temperature (SST) is near 31°C.  Nida is beneath an upper level ridge where the upper level winds are light and there is little vertical wind shear.  Very warm SSTs and little wind shear will allow the circulation of Tropical Storm Nida to consolidate further and it should continue to intensify.  Nida could intensify rapidly once an eye starts to form at the center of circulation.  Tropical Storm Nida will move near or over the northeastern part of Luzon.  Interaction with land could slow or temporarily stop the intensification.  However, Tropical Storm Nida should intensify further after it move wests of the Philippines.

A subtropical ridge north of Nida is steering the tropical storm toward the west-northwest and that general motion is expected to continue.  On its anticipated track Tropical Storm Nida could move over the northern part of Luzon during the next 12 to 24 hours.  Nida could approach the area around Hong Kong as a typhoon in about 48 hours.

The primary threats posed by Tropical Storm Nida to the Philippines are locally heavy rain and flash floods.  Tropical Storm Nida could generate very heavy rain in locations where the circulation causes the wind to blow up the slopes of mountains.  Heavy rain falling on steep terrain in those locations could also cause flash flooding.  Nida could be a typhoon by the time it reaches the part of China near Hong Kong.  Nida will be capable of producing some wind damage and storm surge in addition to heavy rain and flooding when it reaches the coast of China.