Category Archives: Western North Pacific

Western Pacific Typhoons and Tropical Storms

Extremely Powerful Typhoon Meranti Nearing Southern Taiwan

The center of extremely powerful Typhoon Meranti moved closer to the southern end of Taiwan during the past few hours.  At 5:00 p.m. EDT on Tuesday the center of Typhoon Meranti was located at latitude 21.1°N and longitude 121.3°E which put it about 65 miles (105 km) south-southeast of Hengchun, Taiwan.  Meranti was moving toward the west-northwest at 11 m.p.h. (18 km/h).  The maximum sustained wind speed was 190 m.p.h. (305 km/h) and there were wind gusts to 230 m.p.h. (370 km/h).  The minimum surface pressure was 887 mb.

Typhoon Meranti is large and powerful.  The Hurricane Intensity Index (HII) is 46.1.  The Hurricane Size Index (HSI) is 27.9 and the Hurricane Wind Intensity Size Index (HWISI) is 74.0.  As a source of comparison, when Hurriane Katrina was at its peak intensity as a Category 5 hurricane over the Gulf of Mexico in 2005, its HII was 38.6, its HSI was 33.7, and its HWISI was 72.3.  Typhoon Meranti is stronger than Hurricane Katrina was, but Meranti is a little smaller than Katrina was in 2005.  The indices suggest that Typhoon Meranti is capable of causing widespread catastrophic damage.

The circulation of Typhoon Meranti is symmetrical and very well organized.  It possess a tight core consisting of a small inner eye surrounded by a ring of very tall thunderstorms.  A second, larger outer eyewall completely surrounds the inner eye.  The strongest winds are occurring in the inner eyewall near the center of circulation.  Winds to typhoon force are also occurring in the outer eyewall and extend out at least 80 miles (130 km) from the center of circulation.  Additional bands of strong thunderstorms are rotating around the outer eyewall.  Typhoon Meranti is generating strong upper level divergence which is pumping out large quantities of mass and is allowing the surface pressure to be so low.

Typhoon Meranti is probably at its peak intensity.  It is still moving over water where the Sea Surface Temperature is near 31°C.  However, the northwestern edge of the outer eyewall appears to be moving over the southern end of Taiwan.  As more of the circulation moves over Taiwan, there will be some disruption of the airflow.  The center of Typhoon Meranti could move very close to the southern tip of Taiwan.  If the center of Meranti moves over southern Taiwan, then the typhoon will weaken more quickly.  It currently appears that the center of Typhoon Meranti could move just south of the southern tip of Taiwan, and on that track the typhoon would not weaken as quickly.  When Typhoon Meranti moves west of Taiwan, it will move over slightly cooler SSTs before it reaches China.  Meranti will weaken more before it reaches China, but it will still be a significant typhoon when it makes landfall there.

The center of Typhoon Meranti is wobbling a little as the inner eye rotates around inside the outer eyewall.  If one averages the wobbles, then then core of Meranti is moving on a general west-northwesterly track.  On its anticipated track, the center of Typhoon Meranti will pass very near the southern end of Taiwan during the next few hours.  It could turn slightly toward the northwest as it moves west of Taiwan.  Typhoon Meranti could make a landfall on the coast of China between Xiamen and Shantou in about 24 hours.

Typhoon Meranti is an extremely dangerous storm.  It is capable of causing widespread catastrophic wind damage.  In addition, its intensity and size will produce very heavy rainfall, especially on the eastern slopes of the mountains on Taiwan.  Flash flooding is likely.  Typhoon Meranti will also produce heavy rain over eastern China and additional flooding is likely in that region.  Typhoon Meranti will also cause a significant storm surge in low lying coastal areas.

Typhoon Meranti Becomes Equivalent of Cat. 5 Hurricane and Threatens Taiwan

Typhoon Meranti rapidly intensified into the equivalent of a Category 5 hurricane on the Saffir-Simpson Scale as it moved on a course that threatens Taiwan.  At 11:00 a.m. EDT on Monday the center of Typhoon Meranti was located at latitude 19.2°N and longitude 127.6°E which put it about 495 miles (800 km) southeast of Taiwan.  Meranti was moving toward the west-northwest at 14 m.p.h. (23 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.

Meranti is a large dangerous typhoon.  The Hurricane Intensity Index (HII) is 42.2.  The Hurricane Size Index (HSI) is 25.5 and the Hurricane Wind Intensity Size Index (HWISI) is 67.7.  Those indices suggest that Typhoon Meranti is capable of causing widespread catastrophic damage.

The structure of Typhoon Meranti is very well organized.  A well formed circular eye is surrounded by a ring of very tall thunderstorms.  Additional strong spiral bands of thunderstorms are rotating around the core of the circulation.  Typhoon Meranti is generating strong upper level divergence which is pumping out mass in all directions.

Typhoon Meranti is moving through an environment that will allow it to maintain much of its intensity until it reaches Taiwan.  It is moving over water where the Sea Surface Temperature is near 31°C.  The upper level winds are weak and there is not much vertical wind shear.  If a rainband wraps around the existing eye, then an eyewall replacement cycle could temporarily weaken Typhoon Meranti.

A subtropical ridge is steering Typhoon Meranti toward the west-northwest and that general motion is expected to continue for several more days.  On its anticipated track Typhoon Meranti will be very near the southern tip of Taiwan in about 36 hours.  After it moves past Taiwan it is forecast to move into eastern China.

Meranti is an extremely dangerous typhoon.  It is capable of causing widespread catastrophic wind damage.  In addition it will produce very heavy rain and flooding is a serious concern.

Typhoon Meranti Strengthens Quickly Into the Equivalent of a Major Hurricane

Typhoon Meranti intensified rapidly on Sunday into the equivalent of a major hurricane.  At 11:00 p.m. EDT on Sunday the center of Typhoon Meranti was located at latitude 18.1°N and longitude 129.7°E which put it about 650 miles (1050 km) east-southeast of Taiwan.  Meranti was moving toward the west-northwest at 17 m.p.h. (27 km/h).  The maximum sustained wind speed was 130 m.p.h. (215 km/h) and there were wind gusts to 160 m.p.h. (260 km/h).  The minimum surface pressure was 948 mb.

Typhoon Meranti intensified very rapidly on Sunday.  A small, well formed eye developed at the center of Meranti.  A ring of strong thunderstorms surrounds the eye and additional bands of thunderstorms are spiraling around the core of the circulation.  The circulation is very symmetrical.  Thunderstorms in the core of Typhoon Meranti are generating strong upper level divergence which is pumping out large amounts of mass in all directions.  Meranti is a very well organized typhoon.

Typhoon Meranti is moving through a very favorable environment. It is moving over water where the Sea Surface Temperature is near 31°C.  The upper level winds are weak and there is little vertical wind shear.  Meranti will continue to intensify and it could become a Super Typhoon.  If an eyewall replacement cycle occurs, there could be fluctuations in the intensity of Meranti.

A subtropical ridge is steering Typhoon Meranti toward the west-northwest and that general motion is expected to continue for another couple of days.  On its anticipated track Typhoon Meranti will be near northern Luzon, Taiwan and the southern Ryukyu Islands in about 48 hours.  Meranti will be a dangerous typhoon at that time.  It will be capable of significant wind damage.  It will also cause very heavy rain and create the potential for significant flooding.

Tropical Storm Meranti Forms West of Guam

A center of circulation developed within an area of thunderstorms west of Guam on Saturday and the system was designated as Tropical Storm Meranti.  At 5:00 p.m. EDT on Saturday the center of Tropical Storm Meranti was located at latitude 16.0°N and longitude 135.8°E which put it about 1070 miles (1725 km) east-southeast of Taiwan.  Meranti was moving toward the west at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 991 mb.

The circulation of Tropical Storm Meranti is still organizing and the distribution of thunderstorms is asymmetrical.  Most of the thunderstorms are occurring east of the center of circulation.  There is a cluster of the thunderstorms just to the east of the center.  There are also two well formed rainbands east of the core of Tropical Storm Meranti.  Additional spiral bands are located in all parts of the tropical storm.  The thunderstorms near the center are generating upper level divergence which is pumping out mass in all directions.

Tropical Storm Meranti is moving through an environment which is favorable for further intensification.  It is moving over water where the Sea Surface Temperature is near 31°C.  An upper level ridge located to the northwest of Meranti is producing northeasterly winds which are blowing across the western portion of the tropical storm.  The upper level winds are weaker over the eastern half of the circulation and the vertical wind shear is only slowing the intensification.  Although there may be some drier air in the western half of the circulation, Tropical Storm Meranti could intensify into a typhoon on Sunday.  Meranti could become a strong typhoon in two or three days.

A subtropical ridge north of Tropical Storm Meranti is steering it toward the west.  The subtropical ridge is forecast to steer Meranti in a general west-northwesterly direction during the next two or three days.  On its anticipated track Tropical Storm Meranti is expected to approach the area of northern Luzon, Taiwan and the southern Ryukyu Islands in about three days.  It could be a strong typhoon at that time.

Tropical Storm Namtheun Bringing Wind and Rain to Southwest Kyushu

Tropical Storm Namtheun brought wind and rain to southwestern Kyushu on Saturday as the center moved just west of the coast.  At 8:00 p.m. EDT on Saturday the center of Tropical Storm Namtheun was located at latitude 31.4°N and longitude 129.6°E which put it about 85 miles (135 km) south of Nagasaki, Japan.  Namtheun was moving toward the north-northwest at 6 m.p.h. (10 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 985 mb.

Tropical Storm Namtheun has a small, but well organized circulation.  There is the remnant of the eye that existed when Namtheun was a typhoon.  A broken ring of thunderstorms surrounds the remnant eye.  Several spiral rainbands are rotating around just outside the small core of Namtheun.  Winds to tropical storm force extend out about 60 miles (95 km) from the center of circulation.

Tropical Storm Namtheun is moving through an environment that is marginally favorable for a tropical storm.  It is moving over water where the Sea Surface Temperature (SST) is near 29°C.  A large upper level trough is producing southerly winds which are blowing across the top of Tropical Storm Namtheun.  Those winds are generating moderate vertical wind shear and they are inhibiting the upper level divergence to the south of the tropical storm.  The marginally favorable environment could allow Tropical Storm Namtheun to maintain its intensity for another 12 to 24 hours.  After that time it will move over cooler SSTs and start to weaken faster.

The upper level trough is steering Tropical Storm Namtheun toward the north and that general motion is expected to continue for another 12 hours or so.  After that time, southwesterly winds are expected to turn Tropical Storm Namtheun more toward the northeast.  On its anticipated track Tropical Storm Namtheun will move close to Nagasaki, Fukuoka, Kitakyushu and the southwestern portion of Honshu.

Tropical Storm Namtheun’s small size should keep the wind damage minimal.  It could cause locally heavy rainfall and the potential for flooding, but the areal extent of any floods should be limited.

Typhoon Namtheun Heads for Southern Japan

Typhoon Namtheun spun up quickly on Thursday and moved steadily toward Kyushu in southern Japan.  At 11:00 p.m. EDT on Thursday the center of Typhoon Namtheun was located at latitude 26.6°N and longitude 130.8°E which put it about 335 miles (540 km) south of Kagoshima, Japan.  Namtheun was moving toward the north at 7 m.p.h. (11 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.

Typhoon Namtheun developed quickly from a low pressure system along a surface trough.  Namtheun has a small but very well organized circulation.  It has a tiny pinhole eye surrounded by a ring of strong thunderstorms.  Several other rainbands are spiraling around the ring of strong thunderstorms.  The thunderstorms are generating upper level divergence which is pumping out mass in all directions.  The upper level divergence is slightly less to the west of the center of circulation.

Typhoon Namtheun is in an environment favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 30°C.  Although there is a large upper level trough over eastern Asia which contains strong southwesterly winds, Typhoon Namtheun developed east of those strong winds.  It is in an area where the upper level winds are weaker and there is little vertical wind shear.  Namtheun is likely to intensify more during the next day or two.  However, Namtheun’s small circulation means that it will respond very rapidly to positive or negative changes in its surrounding environment.

A ridge to the east of Namtheun is steering the typhoon toward the north and that general motion is expected to continue for several more days.  On its anticipated track Typhoon Namtheun could be very near the southern tip of Kyushu within 48 hours.  It could bring strong winds and heavy rain to parts of southern Japan.

Typhoon Lionrock Nearing Landfall in Japan

An upper level low is pulling Typhoon Lionrock toward a landfall in northern Japan.  At 8:00 p.m. EDT on Monday the center of Typhoon Lionrock was located at latitude 36.1°N and longitude 142.5°E which put it about 150 miles (240 km) south-southeast of Sendai, Japan.  Lionrock was moving toward the north-northwest at 24 m.p.h. (39 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 965 mb.

An upper level low west of Japan was pulling Typhoon Lionrock back toward the west-northwest.  At its current track and speed Typhoon Lionrock would make landfall on the northeastern coast of Honshu near Sendai in about six hours.

The structure of Typhoon Lionrock is changing as a result of cooler Sea Surface Temperatures and more vertical wind shear.  Lionrock is making a transition of a tropical cyclone to an extratropical cyclone.  The circulation is becoming more elongated and the typhoon is pulling cooler drier air into the western half of the circulation.  The wind field will tend to expand as the typhoon becomes extratropical.

Typhoon Lionrock will be capable of producing minor wind damage along its path.  It could also cause locally heavy rainfall and flash floods over northern Honshu.  It will pass over some of the same areas recently affected by Typhoon Mindulle.

Large Typhoon Lionrock Moves Closer to Japan

Large Typhoon Lionrock moved closer to Japan on Sunday.  At 11:00 p.m. EDT on Sunday the center of Typhoon Lionrock was located at latitude 31.1°N and longitude 142.1°W which put it about 385 miles (620 km) south-southeast of Tokyo, Japan.  Lionrock was moving toward the northeast at 19 m.p.h. (31 km/h).  The maximum sustained wind speed was 110 m.p.h. (180 km/h) and there were wind gusts to 130 m.p.h. (210 km/h).  The minimum surface pressure was 952 mb.

Typhoon Lionrock retains a large symmetrical circulation.  Winds to typhoon force extend out about 40 miles (65 km) from the center.  Microwave satellite images suggest that there could be two eyewalls.  The inner eyewall is weaker on the western side and the larger outer eyewall has fewer thunderstorms on the northwestern side.  Other spiral bands are rotating around outside the outer eyewall.  Thunderstorms near the core of the circulation are generating upper level divergence which is pumping out mass primarily to the east of the typhoon.

The environment around Typhoon Lionrock would be marginally favorable for intensification.  Lionrock is moving over water where the Sea Surface Temperature (SSTs) is near 28°C.  An upper level trough west of Lionrock is generating southwesterly winds which are affecting the upper level divergence on the western side of the typhoon.  However, the vertical wind shear is not too significant.  On the other hand, concentric eyewalls often produce weakening as the inner eye wall dissipates and the stronger winds occur in the outer eyewall.  So, Lionrock could maintain a steady intensity or weaken slowly during the next 24 hours.  After that time is will move over cooler SSTs and it could weaken more.

The upper level trough is steering Typhoon Lionrock toward the northeast and that general motion is expect to continue for another 24 hours.  After that time, the upper trough will turn Lionrock back toward the northwest.  On its anticipated track Typhoon Lionrock will make landfall on northeast Honshu north of Tokyo in about 36 hours.  It could cause some wind damage.  Heavy rainfall and flash floods will also pose serious risks since Lionrock will move over some of the same areas affected by Typhoon Mindulle.

Typhoon Lionrock Turns in the Direction of Japan

After meandering southeast of Okinawa for several days Typhoon Lionrock started moving northeast toward Japan on Friday.  At 5:00 p.m. EDT on Friday the center of Typhoon Lionrock was located at latitude 23.7°N and longitude 133.0°E which put it about 920 miles (1485 km) south-southwest of Tokyo, Japan.  Lionrockk was moving toward the northeast at 6 m.p.h. (10 km/h).  The maximum sustained wind speed was 105 m.p.h. (170 km/h) and there were wind gusts to 125 m.p.h. (200 km/h).  The minimum surface pressure was 953 mb.

Typhoon Lionrock is very well organized.  It has a circular eye surrounded by a ring of strong thunderstorms.  Additional well formed spiral bands are rotating around outside the core of Lionrock.  Thunderstorms in the eyewall and spiral bands are generating upper level divergence which are pumping out mass in all directions.  The upper level divergence is inhibited a little on the far northern edge of the circulation by northerly winds impinging on Typhoon Lionrock.  Even so, there is enough upper level divergence to compensate for the strong inflow of mass near the surface and Typhoon Lionrock has been in a nearly steady state during recent hours.

Typhoon Lionrock is moving through an environment that should allow for it to maintain its intensity during the next severall days.  It is moving over water where the Sea Surface Temperature (SST) is near 30°C.  An upper level high over China is generating northerly winds which are effecting the extreme northern edge of the outflow from Lionrock.  However, the vertical wind shear is not very strong and it should have a minimal effect on the intensity of the typhoon in the short term.  Eventually, Typhoon Lionrock will move over cooler SSTs and into a region where the upper level winds are stronger and it will start to weaken before it reaches Japan.

Typhoon Lionrock is moving around the western end of a subtropical ridge and that ridge is beginning to steer it toward the northeast.  That general motion is expected to continue for the next several days.  Eventually Lionrock is forecast to turn more toward the northwest.  On its anticipated track Typhoon Lionrock could approach the eastern coast of Honshu in three or four days.  Lionrock could still be a typhoon at that time.

If Lionrock makes landfall in Honshu as a typhoon it will be strong enough to cause some wind damage.  In addition, Typhoon Lionrock could move over some of the same areas affected by Typhoon Mindulle.  Heavy rain caused by Lionrock could create the potential for additional flash flooding and mudslides.

Lionrock Becomes a Typhoon East of Okinawa

Tropical Storm Lionrock intensified into a typhoon east of Okinawa on Tuesday.  At 8:00 p.m. EDT on Tuesday the center of Typhoon Lionrock was located at latitude 25.3°N and longitude 132.8°E which put it about 340 miles (550 km) east-southeast of Okinawa.  Lionrock was moving toward the south-southwest at 11 m.p.h. (17 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 965 mb.

Lionrock is a fairly small typhoon.  Winds to tropical storm force only extend out about 150 miles (240 km) from the center.  The circulation of Typhoon Lionrock is very well organized.  A small distinct eye is visible on satellite imagery.  The eye is surrounded by a ring of strong thunderstorms.  Additional spiral rainbands are rotating around the core of Lionrock.  The thunderstorms around the eye are generating upper level divergence which is pumping out mass in all directions.

Typhoon Lionrock is in an environment that is favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 30.5°C.  The upper level winds are weak and there is little vertical wind shear.  A small typhoon like Lionrock can intensify very quickly and it appears to be doing so.

An upper level ridge over China is steering Typhoon Lionrock slowly toward the south-southwest and that general motion is expected to continue for another day or two.  Lionrock could move into an area where the steering winds are weak and it could stall for a period of time.  Eventually, an upper level trough is expected to approach the area from the west and begin to pull Lionrock toward the north.