Temperatures are expected to reach 39 degrees Celsius in Nagoya City, 38 in Kyoto City, 37 in Osaka City, 36 in the cities of Kobe and Yokohama, and 35 in Fukuoka City and central Tokyo, the Japan Meteorological Agency (JMA) said.
The JMA and the Environment Ministry have issued heatstroke alerts for 30 prefectures, urging people across the country to take precautions.
The soaring mercury and warm damp air will also cause localised thunderstorms, the JMA added, calling on people to stay vigilant against lightning, gusty winds and hail.
Meanwhile, the weather agency said that severe tropical storm Maria is currently moving north over waters off the eastern coast of Japan and will maintain this course through Monday.
Weather officials said that the sea off the Kanto and Tohoku regions is expected to start turning rough as early as Saturday, with winds also predicted to gather pace.
-- BERNAMA
