Humid or sultry: uncomfortably hot due to high humidity, often making you sweat.
夏は蒸し暑くて夜もよく眠れない。
Summer is so humid that I can't sleep well at night.
今日は蒸し暑いから、冷たい飲み物が欲しい。
It's humid today; I want a cold drink.
エアコンをつけないと部屋が蒸し暑くなる。
Without air conditioning, the room becomes humid and stuffy.
梅雨の時期は蒸し暑い日が続く。
Humid days continue through the rainy season.