Mugginess; the uncomfortable feeling of heat caused by high humidity and temperature — typical of sultry summer weather.
梅雨の時期は蒸し暑さでよく眠れない。
During the rainy season, the muggy heat makes it hard to sleep.
蒸し暑さを和らげるためにエアコンをつけた。
I turned on the air conditioner to relieve the muggy heat.
外の蒸し暑さとは違い、室内は風が通って快適だった。
Unlike the muggy conditions outside, the interior had a breeze and felt comfortable.