It was sunny and hot over wide areas from northern Japan to the Chugoku region on Saturday. Weather officials warn of the dangers of heatstroke, with more heat in the forecast for Sunday as well.

Daytime highs were 37.2 degrees Celsius in Toyooka City, Hyogo Prefecture, 36.8 degrees in Tottori City, and 34.5 degrees in central Tokyo. More than 70 percent of the Meteorological Agency's observation points recorded temperatures of over 30 degrees Celsius.

The mercury is expected to climb across the country on Sunday. Daytime highs are expected to reach 38 degrees Celsius in Kumagaya City in Saitama Prefecture, 37 degrees in the cities of Fukui, Maebashi in Gunma Prefecture, Fukushima and Yamagata, and 35 degrees in central Tokyo.

Meanwhile, Tropical Storm Songda over the East China Sea and moist air around the edge of a high pressure system are making atmospheric conditions unstable in southern Kyushu and Shikoku. Rain clouds are developing locally.

Songda is expected to gradually move away from Japan. But moist air will continue to flow in, bringing heavy rain with thunder to the Shikoku region through late Saturday night and to southern Kyushu through shortly after noon on Sunday. Extremely heavy rain may fall in some areas.

In the 24 hours through Sunday evening, up to 200 millimeters of rain is expected in southern Kyushu, up to 120 millimeters in Shikoku, and up to 100 millimeters in Kanto-Koshin.

The Meteorological Agency is calling on people to be on the alert for landslides, flooding in low-lying areas and swollen rivers, as well as lightning strikes and gusty winds including tornadoes.