When chapter 23 begins, the reader is told that the weather is hot. Really hot.
It was the longest day: mindlessly hot, unspeakably hot, too hot to move or even think.
In addition to being hot, I think the humidity must be really high. The text doesn't explicitly say so, but there are some hints. The reader is told that the air feels heavy with little to no breeze. I've lived in Florida for a little bit of my life, and that state has some ridiculous heat and humidity. When Babbit describes the weather as oppressively hot and heavy, I'm reminded of my time in Florida.
By the time the chapter ends though, the weather has turned. When Winnie wakes up moments before midnight, the reader is told that a thunderstorm is moments away from beginning.
As for what actions happened in Chapter 23, there isn't much to write about. Winnie has been confined to the house and the yard, which is fine because it's too hot to do anything else. The rest of the family tries not to move around too much. Everybody goes to bed early, which suits Winnie just fine, because she is waiting until midnight in order to sneak out and help rescue Mae.