Unstable atmosphere causing downpours in Hokkaido, northern Japan

Weather officials are warning of flooding in low-lying areas and swollen rivers in the northern Japanese prefecture of Hokkaido due to warm and moist southerly air.

The Meteorological Agency said a cold air mass aloft, and hot and humid air coming in along the periphery of a high-pressure system, is causing unstable atmospheric conditions mainly in northern Japan.

It said rainclouds were lingering over southern through western Hokkaido. In the town of Hokuryu, a gauge logged 45 millimeters of rain in an hour through 11:00 a.m. on Tuesday.

The town of Setana, also in Hokkaido, saw 108.5 millimeters of rain in a 6-hour period until 11.00 a.m. That's over 70 percent of the area's normal monthly rainfall for September.

Lightning strikes have been observed in Hokkaido and its neighboring prefecture of Aomori.

Weather officials say unstable atmospheric conditions are expected to remain over northern Japan until late Tuesday night, and the Tokai region in central Japan until the evening. They warn thunderstorms could bring over 50 millimeters of rain per hour in some areas.

They are warning of flooding and swollen rivers, as well as landslides, lightning strikes, tornadoes and hailstorms.

Weather officials are urging people to seek shelter in sturdy buildings if they feel sudden cool winds, which are a sign of approaching thunderclouds.