That is perfectly normal.
The present continuous can always refer to future events, especially they are a direct consequence of the present situation and certain to occur: It is rather like the "going to" future:
I'm playing tennis tomorrow (because the court is booked and its in my diary).
With "hope" the present tense often refers to future events. "
I hope you pass your exam.
If you are hoping for something that will take some time, then present continuous is fine:
I hope I'm leading the parade tomorrow. Coach said he'd pick a leader tonight.
Your example is very natural, with "raining" functioning almost like an adjective to describe the weather.