Japan Records First 40°C+ Day in the Year

Sun Sep 06 2026 11:14:02 GMT+0000 (Coordinated Universal Time)

Japan has hit the first ‘kokushobi’—a cruelly hot day, with temperatures over 40°C—sparking heatstroke alerts, new safety guidance and calls for lighter workwear.

On Tuesday, temperatures in central Japan surpassed 40°C in three cities, marking the first official “kokushobi” day. The hot‑day prompted nationwide heatstroke alerts, the Tokyo Fire Department to issue ambulance overload warnings, and advice to stay hydrated and use air‑conditioning. Experts note a trend of rising extremes, last year’s record high of 41.8°C in Isesaki and record workplace heatstrokes. The Tokyo government is urging office workers, especially men, to wear shorter sleeves and fewer layers to cope with the heat. As the summer heats up, authorities remain on alert for further heat‑related incidents.

Japan’s first “kokushobi”: 40°C+ heatwave rattles the country

Japan experienced its first “kokushobi”, a newly coined weather term meaning a “cruelly hot day”, when temperatures in the central cities of Tajimi, Gujo and Toyoda climbed above 40°C (104°F) on Tuesday.

The Japanese Meteorological Agency (JMA) first introduced the term in April to improve public awareness of dangerous heat days. The agency highlights that days over 35°C are called “moshobi” (extremely hot), while the harsher “koku” (cruel) qualifier designates temperatures that push people into heat‑stroke risk.

In total, almost 300 of the country’s 914 observation stations recorded a “moshobi” this Tuesday, according to Kyodo News.

In response, authorities have issued heat‑stroke alerts in more than 40 prefectures and advised residents to use air‑conditioners, drink plenty of water, and maintain proper salt intake. The Tokyo Fire Department recorded 287 cases of suspected heatstroke that day, the highest for the year, and subsequently issued an ambulance‑overload warning.

Last year Japan recorded a historic 41.8°C in Isesaki, and workplace‑related heatstrokes topped 1,800 cases. The Tokyo government is urging male office workers to adopt casual attire—T‑shirts and shorts—to mitigate heat exposure, though the move has sparked debate over workplace dignity and personal preference.

With the heat is expected to persist, JMA warns that another scorching week may follow. Residents are urged to monitor local alerts, stay indoors during peak temperatures, and ensure safe hydration habits. As the summer climbs higher, Japan’s new weather terminology may become an essential part of everyday safety communication.