It's not the heat, it's the humidity proverb
Used to mean that it is the high humidity that makes a person uncomfortable rather than the degree of heat
A: I feel that summer in the south is much hotter than in the north. B: Well, it's not the heat, it's the humidity.
Rainy, wet weather
If the heavens open, it starts to rain heavily.
Intensely hot and irritated
A heavy rain
Wonderful weather, particularly on a day when an outdoor event is scheduled