Japan has introduced a new official term for days when temperatures exceed 40 degrees Celsius, as the country experiences increasingly frequent extreme heat conditions.
The Japan Meteorological Agency announced on April 17 that the new classification, “kokushobi,” meaning “severely hot day,” will now be included in official weather forecasts following expert discussions and an online public survey.
The agency said the decision was made in response to a rising number of days surpassing the 40°C threshold in recent years, prompting the need for a clearer public warning category for extreme heat conditions.
“Kokushobi” joins an existing set of official temperature-related terms used in Japanese weather reporting, including “natsubi” for days above 25°C, “manatsubi” for days above 30°C, and “moshobi” for days above 35°C.
The term was selected from 13 proposed candidates in a survey conducted between February and March, reflecting both public input and expert recommendations.
According to the agency’s data, Japan has recorded 108 days above 40°C since records began in 1872, with 41 of those occurring between 2023 and 2025 alone—highlighting a sharp recent increase in extreme heat events.
Officials said the new classification aims to improve public awareness and preparedness as climate patterns continue to shift.
