Tag Archives: Tropical Depression 15W

Typhoon Koinu Moves Southeast of Hong Kong

Typhoon Koinu moved southeast of Hong Kong on Friday night. At 11:00 p.m. EDT on Friday the center of Typhoon Koinu was located at latitude 21.1°N and longitude 115.3°E which put it about 115 miles (185 km) southeast of Hong Kong. Koinu was moving toward the west-southwest at 4 m.p.h. (6 km/h). The maximum sustained wind speed was 120 m.p.h. (195 km/h) and there were wind gusts to 150 m.p.h. (240 km/h). The minimum surface pressure was 952 mb.

Typhoon Koinu intensified back to the equivalent of a major hurricane over the South China Sea southeast of Hong Kong on Friday. A circular eye with a diameter of 12 miles (19 km) was at the center of Koinu’s circulation. The eye was surrounded by a ring of thunderstorms and the strongest winds were occurring in that ring of storms. Bands of showers and thunderstorms revolved around the core of Typhoon Koinu. Storms near the core generated upper level divergence that pumped mass away from the typhoon.

Wins to typhoon force extended out 40 miles (65 km) from the center of Typhoon Koinu. Winds to tropical storm force extended out 285 miles (460 km) in the northeast quadrant of Koinu’s circulation. Winds to tropical storm force extended out 130 miles (210 km) in the other parts of Typhoon Koinu. The Hurricane Intensity Index (HII) for Typhoon Koinu was 22.1. The Hurricane Size Index (HSI) was 14.9 and the Hurricane Wind Intensity Size Index (HWISI) was 37.0. Typhoon Koinu was similar in size and intensity to Hurricane Harvey when Harvey hit Texas in 2017.

Typhoon Koinu will move through an environment somewhat favorable for a strong typhoon during the next 24 hours. Koinu will move over water where the Sea Surface Temperatures are near 28°C. It will move under the southern part of an upper level ridge over China. The ridge will produce easterly winds that will blow toward the top of Koinu’s circulation. Those winds will cause some vertical wind shear. The wind shear will inhibit intensification. The circulation around the northern side of Typhoon Koinu could draw in some drier air from China. Typhoon Koinu could maintain its intensity during the next 24 hours if the drier air does not reach the inner core of the circulation. Koinu is likely to weaken if the drier penetrates to the core of the circulation.

Typhoon Koinu will move will move around the southern part of a high pressure system over eastern Asia. The high pressure system will steer Koinu slowly toward the west-southwest during the next 24 hours. On its anticipated track the center Typhoon Koinu will move south of Hong Kong on Saturday.

Elsewhere over the Western North Pacific Ocean, Tropical Depression 15W formed east-southeast of Guam. At 11:00 p.m. EDT on Friday the center of Tropical Depression 15W was located at latitude 9.9°N and longitude 154.2°E which put it about 700 miles (1130 km) east-southeast of Guam. The tropical depression was moving toward the west-northwest at 13 m.p.h. (21 km/h). The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h). The minimum surface pressure was 1003 mb.

Tropical Storm Wukong Forms Southeast of Japan

Tropical Storm Wukong formed southeast of Japan on Monday.  At 5:00 p.m. EDT on Monday the center of Tropical Storm Wukong was located at latitude 29.0°N and longitude 159.0°E which put it about 1370 miles (2210 km) east-southeast of Tokyo, Japan.  Wukong was moving toward the north at 24 m.p.h. (39 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and the were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 984 mb.

A cluster of thunderstorms developed southeast of Japan during the weekend and a low level center of circulation formed near the southwestern edge of the cluster of storms.  However, strong upper level winds blowing from the southwest kept blowing the top of the circulation northeast of the low level center and the system was unable to develop.  The upper level winds slowed on Monday and a band of showers and thunderstorms wrapped around the northern and western sides of the center of circulation.  The Japan Meteorological Agency designated the system as Tropical Storm Wukong.

The circulation of Tropical Storm Wukong organized quickly after the upper level winds weakened.   As mentioned above, a primary rainband wrapped around the northern and western sides of the center of circulation.  Storms in the primary rainband generated upper level divergence which was pumping mass away to the north of the tropical storm.  Several other bands of showers and thunderstorms developed in the eastern half of the circulation.  Bands south and west of the center consisted primarily of showers and lower clouds.

Tropical Storm Wukong will move through an environment favorable for intensification during the next day or so.  Wukong will move over water where the Sea Surface Temperature is near 27°C.  Wukong is moving along the eastern portion of an upper level trough.  The trough is producing southwesterly winds which are blowing toward the top of the circulation.  However, those winds weakened on Monday and they will not cause enough vertical wind shear to prevent further intensification.  Tropical Storm Wukong could strengthen into a typhoon during the next 24 to 36 hours.  Eventually, Wukong will move over cooler water and it will begin to weaken.

Tropical Storm Wukong is moving between an upper level trough to the west and an upper level ridge to the east.  The trough and ridge were combining to steer Wukong toward the north and a general northerly motion is expected to continue.  On its anticipated track Tropical Storm Wukong will stay west of the larger islands of Japan.  Wukong could approach the Kuril Islands in about three days.

Elsewhere over the Western North Pacific former Tropical Storm Ampil weakened to a tropical depression over land southeast of Beijing, China, Tropical Storm Son-tinh meandered near the coast of southeastern China and Tropical Depression 15W organized southwest of Iwo To, Japan.  At 5:00 p.m. EDT on Monday the center of Tropical Depression Ampil was located at latitude 38.8°N and longitude 117.6°E which put it about 110 miles (175 km) southeast of Beijing, China.  Ampil was moving toward the north-northwest at 18 m.p.h. (29 km/h).  The maximum sustained wind speed was 35 m.p.h. (55k km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 998 mb.  Tropical Depression Ampil was still dropping locally heavy rain over parts of eastern China.

At 5:00 p.m. EDT on Monday the center of Tropical Storm Son-tinh was located at latitude 21.2°N and longitude 109.0°E which put it about 40 miles (65 km) southeast of Beihai, China.  Son-tinh was moving toward the west-northwest at 6 m.p.h. (10 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 Son-tinh was dropping locally heavy rain over parts of southeastern China and Hainan Island.

At 5:00 p.m. EDT on Monday the center of Tropical Depression 15W was located at latitude 17.6°N and longitude 136.3°E which put it about 585 miles (945 km) southwest of Iwo To, Japan.  It was moving toward the north-northwest at 10 m.p.h. (16 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 998 mb.  The circulation of Tropical Depression 15W became more organized on Monday and it could eventually strengthen into a typhoon when it moves toward Iwo To later this week.