Japan Logs First 'Cruelly Hot Day' as Heat Rises

Japan’s first cruelly hot day has arrived, with the country’s new heat warning term now matching a dangerous reality. Temperatures climbed above 40C in three central Japanese cities on Tuesday, prompting fresh concern as the heatwave stretches on and officials brace for more severe weather next week.

The Japan Meteorological Agency introduced the term in April to describe days when temperatures reach 40C, using it as a sharper warning for the public. On Tuesday, Tajimi, Gujo and Toyota all crossed that line. The agency said the heat is expected to continue into next week, underscoring how Japan’s summer heat is no longer a short-lived discomfort but a growing public safety issue.

Japan already uses separate labels for hotter days above 25C, 30C and 35C. Days above 35C are called moshobi, or extremely hot days. The new kokushobi label goes a step further, with the word koku meaning harsh or cruel. That distinction matters because the country is trying to communicate risk more clearly as extreme weather becomes more intense around the world.

The scale of the heat was clear beyond the three cities that hit 40C. Kyodo News reported that nearly 300 of Japan’s 914 observation points recorded a moshobi on Tuesday. At the same time, authorities issued heatstroke alerts in more than 40 prefectures. Officials advised people to use air-conditioners, drink enough water, take in salt and avoid long periods outdoors.