Japan Meteorological Agency Gives Official Name to 40 C-Plus Days as Intense Heat Increase

The Yomiuri Shimbun

12:14 JST, April 17, 2026

Days when the temperature exceeds 40 C will be given a new name, the Japan Meteorological Agency announced on Friday.

The agency made the decision based on the results of an online survey and the opinions of experts.

The new word — “kokushobi,” which can be translated as “severely hot day” — is now part of the lexicon used in weather forecasts.

Other official words used in the forecasts are “natsubi” (summer day) for days higher than 25 C, “manatsubi”(midsummer day) for days higher than 30 C and “moshobi” (extremely hot day) for days higher than 35 C.

The new word was included in the lexicon due to a recent high frequency of days exceeding 40 C.

In the survey, which ran from February through March, the agency included 13 candidates for the new word, including the one that was chosen.

According to the agency, there have been 108 days when the temperature has exceeded 40 C since statistics began in 1872. Of these, 41 days occurred between 2023 and 2025.