John Knowless chose to start the book in mid november during a rain storm. The benefits that he got from that setting, were that it help to form the basic feel of the story. If Knowles had started the story in a sunny august setting, the story would be more fast paced; Gene wouldn't have to dodge puddles or get his shoes dirty, and the imagery wouldn't develop as well.
Overall i believe that Knowles was attempting to get the readers more comfortable with the beginning of a new book, as well as attempting to help the readers imagine the novels tones and styles.