This is the 9164th most frequent Japanese word.
熱気
"熱気" means "heat, warmth, or enthusiasm."
Here, '熱気' is used to describe the literal heat of summer in the environment outside.
夏の熱気が外にいると感じられる。
The summer's heat can be felt when being outside.
In this sentence, '熱気' refers to the intense atmosphere or enthusiasm felt in a location where an event is taking place.
会場の熱気がすごいです。
The enthusiasm of the venue is amazing.
In this context, '熱気' indicates the warm air or heat that spreads into a space, causing a change in temperature.