This is the 9742nd most frequent Japanese word.
蒸し暑い
Humid and hot.
In this sentence, '蒸し暑い' describes the characteristically muggy (hot and humid) weather condition, expressing that the speaker feels it today.
今日は蒸し暑いので、さっぱりした飲み物が欲しいです。
It's muggy today, so I want a refreshing drink.
Here, '蒸し暑い' defines a specific condition for the day, namely the presence of mugginess, influencing the described preference for physical activity.
彼は蒸し暑い日に運動するのが好きです。
He likes exercising on muggy days.
In this case, '蒸し暑い' is used to characterize the interior environment of a room, implying that its mugginess impacts the ease of studying within.