It's a great river to run anytime of year.
Here's a link you might find helpful:
The link lists out three sections, the last is the most popular and has the rapids. The lower half of the page lists out the rapids you'll encounter on that 3rd stretch from West Table down to Sheep's Gulch.
In August it's a fairly tame float with a couple OK rapids - excellent for kayaking, tame for rafting. But the scenery on all the sections is fantastic, the weather should be decent. Afternoons can bring small rainshowers and some wind, evenings are nice when most people are off the water. Like anywhere, Fri/Sat/Sun will be the busiest days.
The flow of those sections in August will likely be around 4,000 -5,000 CFS, considered lower water. The river cuts through a deep channel - plenty of dive in and swim possibilities, especially on Section #3.
I've taken I've taken friends and family down in a 14' raft with kids as young as 2 no problem. The outfitters PACK their rafts full of people - as efficient as an amusement park.
If running the lower stretch (#3), heads up for the rangers running the boat ramps/parking lots. Launch and take out at the private side and keep a cool head and the rangers will be cool back. They put up with a lot of crap while trying to keep the throngs semi organized and out of the outfitters' way
Enjoy the river.