Tropical Storm Yun-yeung is traveling north-northeast over the sea south of Japan. It may approach eastern Japan and make landfall on Friday.
Japan's meteorological agency says Yun-yeung was traveling at about 25 kilometers per hour as of 9 a.m. on Thursday.
Extremely heavy rain accompanied by thunder is expected in eastern and northern Japan through Saturday.
Bands of heavy rain clouds may form around the Izu Islands in the Pacific south of Tokyo from Thursday night through Friday morning, which could drastically increase the risk of disasters.
In the 24 hours through Friday noon, as much as 250 millimeters of rain is expected in the Tokai region and the Izu Islands, and 150 millimeters in the Kanto-Koshin region.
In the 24 hours through Saturday noon, 100 to 200 millimeters of rain may fall in Kanto-Koshin, 100 to 150 millimeters in the Tohoku region, and 50 to 100 millimeters in Tokai and the Izu Islands. Some areas may get more rainfall if bands of heavy rain clouds form.
Weather officials are warning of possible mudslides, floods in low-lying areas and swollen rivers. They are also urging caution against lightning strikes, tornadoes and strong gusts.