The Japan Meteorological Agency's heat classification system includes 'natsubi' for temperatures above 25°C, 'manatsubi' for 30°C, and 'moshobi' for 35°C. Of the 108 days on record above 40°C in Japan since 1872, as many as 41 occurred between 2023 and 2025, and 132 of 153 meteorological stations recorded new highs in 2025. 8°C was set, 30 locations across 13 prefectures reported temperatures above 40°C.
The agency picked 'kokushobi', which roughly translates as 'severely hot day', after an online survey in February and March that offered 13 candidates, combined with expert opinion, though the specific criteria for selection remain unclear. 73°C. Scientists attribute much of Japan's warming to the climate crisis, particularly the warming of waters around the Japanese archipelago which traps the country in an elevated heat well into autumn, and warmer oceans also fuel heavier rainfall and more intense typhoons.
1°C, 96 Tokyo residents died from suspected heatstroke over a single month. Another record-breaking summer is forecast for Japan in 2026, though exact projections are not specified, and experts project that the trend of extreme heat will continue. Researchers warn that spring and autumn in Japan are increasingly being squeezed out by an extended summer heat season, and if the climate crisis marches on unabated, Japan risks losing its cherished four seasons, becoming a country with only two, a pattern seen across Asia.