We will be out there almost the exact same time. Last time we went we got some pretty heavy rain. RSR was closed off and on the whole time. No point in even waiting in line because it would open/close randomly. Some people spent their whole day trying to get on it. Plan for eating as well - everything gets soaked. You're going to want indoor eating if you don't like soggy food. The other rides people have mentioned were also closed.
Here's the thing we didn't plan on though - YOU will get soaked. Your clothes, jackets, strolled, bags - whatever you have, is going to get completely soaked. We brought jackets and thought we would be fine. NO. Miserable, wet, and cold. Poncho's help, but in a sustained rain, they can only do so much. Every time you sit your legs and butt will get soaked. This year we are going to bring some real rain suits, covering tops like a jacket, and bottom like rain pants.
Take my advice, plan for that. You'll be better off than 90 percent of people who's only plan in the poncho.