Former Tropical Storm Namtheun strengthened to a typhoon over the Western North Pacific Ocean north of Wake Island on Saturday morning. At 5:00 a.m. EDT on Saturday the center of Typhoon Namtheun was located at latitude 31.4°N and longitude 165.6°E which put it about 800 miles (1290 km) north of Wake Island. Namtheun was moving toward the north-northeast at 18 m.p.h. (29 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. (150 km/h). The minimum surface pressure was 979 mb.
Former Tropical Storm Namtheun passed over water where the Sea Surface Temperatures are near 27˚C during the past 24 hours and it was able to extract enough energy to strengthen to a typhoon. A small eye formed at the center of Typhoon Namtheun. The eye was surrounded by a broken ring of thunderstorms and the strongest winds were occurring in that ring of storms. Storms near the center of Namtheun generated upper level divergence that pumped mass away from the typhoon. The circulation around Typhoon Namtheun was relatively small. Winds to typhoon force extended out 20 miles (30 km) from the center of Namtheun. Winds to tropical storm force extended out 115 miles (185 km) from the center of circulation.
An upper level trough east of Japan will steer Typhoon Namtheun toward the north-northeast during the weekend. On its anticipated track Namtheun will move toward the Aleutian Islands. Typhoon Namtheun will move into an environment unfavorable for intensification during the weekend. Namtheun will move over much cooler water. The upper level trough east of Japan will produce strong southwesterly winds that will blow toward the top of Namtheun’s circulation. Those winds will cause moderate vertical wind shear. The combination of cooler water and more vertical wind shear will cause Typhoon Namtheun to make a transition to an extratropical cyclone as it moves toward the Aleutian Islands.