TOKYO - Japan was preparing for Typhoon Vongfong on Friday, with the most powerful storm of the year packing winds gusting up to 156 mph as it powered north toward the Okinawa island chain that is home to U.S. military bases. Vongfong was downgraded from a "super typhoon" by the Joint Typhoon Warning Center Friday but was still the equivalent of a Category 3 hurricane, threatening to dump up to 19 inches of rain on Okinawa.

Vongfong was south of Okinawa at 3 p.m. local time (2 a.m. ET) Friday as it moved across the Pacific Ocean east of Taiwan and the Philippines, the Japan Meteorological Agency said. It is expected to pass by Okinawa at about midnight Saturday local time (11 a.m. Saturday ET) before skimming southeast of Kyushu Island and weakening. It is expected to hit western mainland Japan on Monday, when businesses and schools are closed for a national holiday, and reach the Tokyo on Tuesday. All air bases on Okinawa were placed on alert for the storm Friday. The eye of the storm will be 17 miles wide when it passes 24 miles northeast of Kadena Air Base on Okinawa at about 2 a.m. local time Sunday (1 a.m. Sunday ET), according to the Stars and Stripes Pacific storm tracker. “There is no question that it is an extremely large, extremely powerful typhoon,'' an official at Japan's Meteorological Agency told Reuters. Its strength has been compared to Typhoon Haiyan, which lashed the Philippines in 2013, leaving 8,000 people dead or missing.

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Super Typhoon #Vongfong seen Oct 9 as it moved north through the Philippine Sea. Latest: http://t.co/7zk27CuVcg pic.twitter.com/TTKns0Uob3 - NASA (@NASA) October 9, 2014

- Arata Yamamoto and Alastair Jamieson