Japanese weather authorities warn that a tropical depression south of Okinawa will strengthen as it heads north, and could affect many areas including western Japan by Friday.
The Japan Meteorological Agency says the depression is expected to move toward Okinawa's main island on Wednesday night, and then north along the Amami Islands, approaching the Pacific coast of western Japan on or after Thursday morning.
It also says moist air flowing toward a front near the island of Kyushu has produced rain clouds over Okinawa's main island and Kyushu.
Landslide warnings have been issued for parts of Okinawa's main island after torrential rain continued in the morning.
In Shibushi, Kagoshima Prefecture, 49 millimeters of rain was logged from 10-11 a.m. on Wednesday.
Weather officials warn that heavy thunderstorms may hit Okinawa, Amami and western Japan, with localized rain exceeding 50 millimeters an hour from Wednesday through Friday.
As much as 250 millimeters of rain is expected in southern Kyushu over 24 hours, through Thursday morning.
The Meteorological Agency is calling for extreme caution against landslides, floods in low-lying areas and swelling rivers. Officials are urging people to follow the latest forecasts.
The Agency says the rainy season has started in northern Kyushu, and the Shikoku, Chugoku and Kansai regions. It's the latest start of the season since 1951, the year in which the earliest records are available.