Typhoon Koinu brought wind and rain to Taiwan on Wednesday night. At 11:00 p.m. EDT on Wednesday the center of Typhoon Koinu was located at latitude 22.1°N and longitude 120.6°E which put it about 10 miles (15 km) west of Hengchun, Taiwan. Koinu was moving toward the west-northwest at 5 m.p.h. (8 km/h). The maximum sustained wind speed was 125 m.p.h. (200 km/h) and there were wind gusts to 155 m.p.h. (250 km/h). The minimum surface pressure was 945 mb.

Typhoon Koinu brought strong winds and heavy rain to southern Taiwan on Wednesday night. The eye of Koinu passed over the southern tip of Taiwan. The northern half of the eyewall moved across southern Taiwan. Typhoon Koinu was the equivalent of a major hurricane when it moved across Taiwan. Winds to typhoon force extended out 70 miles (110 km) from the center of Koinu’s circulation. Winds to tropical storm force extended out 230 miles (370 km) from the center of circulation. The Hurricane Intensity Index (HII) for Typhoon Koinu was 23.6. The Hurricane Size Index (HSI) was 21.6 and the Hurricane Wind Intensity Size Index (HWISI) was 45.2. Typhoon Koinu was stronger than Hurricane Rita was when Rita hit southwest Louisiana in 2005. Koinu was a little smaller than Rita was.

Easterly winds blowing around the northern side of Typhoon Koinu will rise up the eastern slopes of mountains in Taiwan. The enhanced rising motion will produce very heavy rainfall on those eastern slopes. The heavy rain is likely to cause flash floods in some locations.

Typhoon Koinu will move will move around the southern part of a high pressure system over eastern Asia and the Western North Pacific Ocean. The high pressure system will steer Koinu toward the west during the next 24 hours. On its anticipated track the center Typhoon Koinu will move over the South China Sea on Thursday.

The core of Typhoon Koinu was partially disrupted when the eye and northern part of the eyewall moved across southern Taiwan. The disruption of the inner core of Koinu’s circulation is likely to cause Typhoon Koinu to weaken during the next 24 hours even though Koinu will move through an environment favorable for intensification. 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 little vertical wind shear, but the wind shear will not be too strong. Typhoon Koinu is likely to weaken gradually during the next 24 hours because of the disruption of its inner core.