The storm, Typhoon Usagi, approached the straits between the Philippines and Taiwan on Friday as a category 5 storm, the most powerful on the Saffir-Simpson scale used for measuring the force of hurricanes in the Atlantic Ocean. In the Pacific, exceptionally strong typhoons are rated as severe typhoons or even super typhoons, and Typhoon Usagi, with sustained winds of more than 155 miles per hour, briefly qualified as a super typhoon before being downgraded to a severe typhoon.

By Sunday afternoon in Hong Kong, Usagi had already weakened to category 2 storm, with winds of 96 to 110 miles per hour, and had veered toward the Chinese mainland northeast of the city, according to projections by Tropical Storm Risk, a forecasting service based in London. The service forecast that the storm would weaken further to a category 1 after making landfall, but was still nearly certain to bring hurricane-force winds to the territory, which Britain returned to Chinese rule in 1997.