"Summer humidity" refers to the amount of moisture or water vapor present in the air during the summer season. It describes the sticky or muggy feeling that can be experienced when there is a high level of humidity in the atmosphere. Full definition
I can not tell you how hot I have been since the weather abruptly went from comfortable spring temperatures to dead of summer humidity. (aleciamariana.com)
In summer the humidity always wins — but not this summer, baby! (meijerstyle.com)
Summer humidity levels are often controlled with air conditioning. (energyvanguard.com)