lingering summer heat; late-summer heat
Refers to the hot weather that continues after the traditional start of autumn (立秋, around August 7). Commonly used in seasonal greetings and weather reports.
See also: 立秋
残暑が厳しいですね。
The lingering summer heat is intense, isn't it?
残暑見舞いを送る。
Send a late-summer greeting card.
Even in September, the lingering summer heat continues.
This year the lingering summer heat is severe, and it just won't cool down.
In this season of lingering summer heat, how have you been getting on?