The best place to look for the description of the first week of August is in the first paragraph of the prologue.
The words that Babbitt uses in that paragraph are all words that help the reader envision the season and feel hot, humid, sticky, and gross. I do not enjoy heat and humidity, so that paragraph is an awful read for me. It just makes me feel gross. Not only that, but Babbitt writes the paragraph in a way that makes it seem like the heat will last entirely too long.
For example, in the first two sentences the following words are used: "hang," "long," "motionless," and "pauses." Nothing about those words suggests relief from the heat.
As for words that describe the actual heat, here are a few of them: "hot," "balmy," "breathless," "glaring," and "smeared." It's so hot that it takes your breath away. "Balmy" and "smeared" make me think of moisture and humidity. Everything is dripping with hot moisture. I'm sure the windows have condensation streaks on them the entire day. There are not likely any clouds either, which is why the sun is "glaring." The paragraph does say that at night there are storm clouds, but they bring "no relieving rain."
For me, Babbitt paints a picture of some of the worst weather that I can think of.