hot summer day
General term for a day that feels hot in summer, without a strict temperature definition.
Today Tokyo had its first hot summer day of the year.
Today is a hot summer day; stepping outside makes you sweat.
day with max temp ≥ 25°C
Meteorological definition: a day when the highest temperature reaches 25°C or above. Compare with 真夏日 (≥30°C) and 猛暑日 (≥35°C).
This year, the first day with a high of 25°C came earlier than usual, exceeding 25°C in April.
Hot summer days have continued since last week, and I feel sluggish.
That region recorded a hot summer day even though it was March.
夏日 starts at 25°C, but 猛暑日 is reserved for the most extreme days with a high of 35°C or above.
Sunday · nth day of the month; date suffix · counter for days; number of days · Japan
Compound of 夏 (summer) and 日 (day). The meteorological sense is a modern technical usage.