Former Tropical Storm Koinu strengthened to a typhoon over the Western North Pacific Ocean east-southeast of Taiwan on Sunday morning. At 11:00 a.m. EDT on Sunday the center of Typhoon Koinu was located at latitude 18.6°N and longitude 128.5°E which put it about 570 miles (920 km) east-southeast of Hengchun, Taiwan. Koinu was moving toward the northwest at 7 m.p.h. (11 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. (165 km/h). The minimum surface pressure was 977 mb.

Former Tropical Storm Koinu intensified rapidly during the past 24 hours. The inner end of a rainband wrapped around the center of Typhoon Koinu. A circular eye with a diameter off 17 miles (28 km) developed 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 were revolving around the center of Typhoon Koinu, Storms near the center generated upper level divergence that pumped mass away to the west of the typhoon. Winds to typhoon force extended out 20 miles (30 km) from the center of Koinu’s circulation. Winds to tropical storm force extended out 85 miles (135 km) from the center of circulation.

Tropical Storm Koinu will move through an environment favorable for intensification during the next 24 hours. Koinu will move over water where the Sea Surface Temperatures are near 30°C. ‘ It will move under the southeastern part of an upper level ridge centered west of Taiwan. The ridge will produce northeasterly 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, but the shear will not be strong enough to completely stop intensification. Typhoon Koinu will intensify during the next 24 hours. Koinu could strengthen to the equivalent of a major hurricane.

Tropical Storm Koinu will move around the southern part of a high pressure system over eastern Asia. The high pressure system will steer Koinu toward the northwest during the next 24 hours. On its anticipated track Tropical Storm Koinu will move closer to Taiwan. Koinu could approach southern Taiwan in three days. Typhoon Koinu is likely to be the equivalent of a major hurricane when it approaches Taiwan.