Heavy rainfall is forecast for areas along the Pacific coast from southwestern to northern Japan through Tuesday.
The Japan Meteorological Agency says a low-pressure system involving a weather front is causing rain clouds to develop over the regions of southern Kyushu, Kinki and Tokai.
During the one-hour period through 5 a.m. on Monday, 15 millimeters of rain was observed in part of Tsu city in Mie Prefecture and 12.5 millimeters in Kyoto city.
The front and the low-pressure system are expected to move along the southern coast of western to eastern Japan through Tuesday, bringing thundershowers in some places. More than 50 millimeters of rain will likely fall in an hour.
Expected rainfall during the 24-hour period through Tuesday morning is up to 120 millimeters in the Kantokoshin and Tokai regions, 100 millimeters in Tohoku, and 80 millimeters in southern Kyushu and Amami.
The wet weather will continue in Tohoku, which is expected to receive 50 to 100 millimeters of rainfall during the 24-hour period through Wednesday morning.
Agency officials are warning of possible landslides, flooding of low-lying areas and swollen rivers.