A typhoon is a mature tropical cyclone that develops in the northwestern part of the Pacific Ocean between 180° and 100°E. This region is referred to as the northwest Pacific basin. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern (North America to140°W), central (140°W to 180°), and western (180° to 100°E). Identical phenomena in the eastern north Pacific are called hurricanes, with tropical cyclones moving into the western Pacific re-designated as typhoons. The Regional Specialized Meteorological Center (RSMC) for tropical cyclone forecasts is in Japan, with other tropical cyclone warning centers for the northwest Pacific in Honolulu (the Joint Typhoon Warning Center), thePhilippines, and Hong Kong. While the RSMC names each system, the main name list itself is coordinated amongst 18 countries who have territories threatened by typhoons each year. The Philippines uses their own naming list for systems which approach the country.
Within the northwestern Pacific there are no official typhoon seasons as tropical cyclones form throughout the year. Like any tropical cyclone, there are six main requirements for typhoon formation and development: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low pressure center, a pre-existing low level focus or disturbance, and low vertical wind shear. The majority of storms form between June and November whilst tropical cyclone formation is at a minimum between December and May. On average, the northwestern Pacific features the most numerous and intense tropical cyclones globally. Like other basins, they are steered by the subtropical ridge towards the west or northwest, with some systems recurving near and east of Japan. The Philippines receive a brunt of the landfalls, with China and Japan being impacted slightly less. Some of the deadliest typhoons in history have struck China. Southern China has the longest record of typhoon impacts for the region, with a thousand year sample via documents within their archives. Taiwan has received the wettest known typhoon on record for the northwest Pacific tropical cyclone basin.