noun
extremely hot day; day with max temp ≥ 35°C
Official Japanese meteorological term for a day when the maximum temperature reaches 35°C or higher. Often used in weather forecasts and news.
今日は猛暑日になる見込みです。
Today is expected to be an extremely hot day (max temp ≥ 35°C).
今年は猛暑日が続いています。
This year, extremely hot days have been continuing.
真夏日 is a day with a maximum temperature of 30°C or higher, one step below 猛暑日.
Compound of 猛暑 (intense heat) and 日 (day). The term is a modern meteorological classification.