High temperature combined with high humidity; describes hot and muggy conditions (typical of summer in many regions).
夏は高温多湿で熱中症に注意が必要だ。
In summer, high temperatures and humidity require caution against heatstroke.
高温多湿の環境が続くと家の中にカビが生えやすい。
If hot and humid conditions persist, mold is more likely to grow inside the house.
エアコンは高温多湿の時期に大いに役立つ。
Air conditioners are very useful during hot and humid periods.