Why do you think Atticus has his sister come to stay with the children? What are the denotative and connotative meanings of his remark that “the summer’s going to be a hot one”

Atticus knew that he'd be extra busy with the trial, thus, Aunt Alexandra's visit would provide supervision for Jem and Scout.

As far as the summer.... the stress and tension created by the trial would make it a "hot one".