Warm and damp air has destabilized atmospheric conditions in northern Kanto, prompting weather officials to issue information on record hourly rainfall for some areas in Tochigi Prefecture, north of Tokyo.
Japan's Meteorological Agency says extremely unstable atmospheric conditions caused rainclouds to develop over northern Kanto and southern Tohoku on Monday.
Weather radar shows the area around the town of Shioya had about 110 millimeters of rain in the hour through 4:50 p.m. on Monday.
Likewise, areas around the cities of Utsunomiya and Sakura in Tochigi Prefecture had about 110 millimeters of rain in the hour through 3:30 p.m.
Roughly the same amount of rainfall was observed around Utsunomiya City and Haga Town in the hour through 1:00 p.m.
The agency issued a record hourly rainfall information for these areas.
Utsunomiya City had record rainfall of 130.5 millimeters during the three hours ending at 2:50 p.m.
Risks of mudslides have sharply risen in Tochigi prefecture. Authorities have issued mudslide alerts for this area.
Unstable atmospheric conditions are likely to continue until late Monday night in northern Kanto, and Tuesday in Tohoku, and may bring heavy rain with thunder.
Northern Kanto may see extremely heavy rain.
Hokkaido may also experience sudden thunderstorms and gusts through Tuesday.
Weather officials are warning of mudslides, floods in low-lying areas and swollen rivers, as well as gusts and hail.
Meanwhile, a tropical depression over waters south of Japan is expected to develop into a typhoon on Tuesday.
The storm is expected to take a northerly course, and may approach eastern Japan as early as Thursday.