I've been to Mexico in August, many many times. I've been chased out of Cancun by a hurricane and I've been chased out of Florida twice, once out of Key West and once out of just north of Miami. As Jazz points out you're rolling the dice going to the tropics in hurricane season. Personally I'd say pick a spot you want to go and buy travel insurance, make sure it covers hurricanes. Some policies are getting tricky and covering just about everything but a hurricane.
I currently live in the state of Yucatan. I'm about 3 hrs from Cancun and the Costa Maya. I'm on the gulf side of the Yucatan Pen. When a hurricane hits Cancun or Belize it has to cross land to get here. By the time it gets here it's usually just a bunch of rain. So here is a viable option, but keep in mind Merida and the area in general isn't anything like Cancun or the other resort areas. The beach, which is at Progreso and where I live, are not as clean and the water is not as clear. The only real full service beach resort, The Reef Club, bills it's self a 4 star. I've been there it's more like a low 3 star. Merida itself has many very nice hotels, many easily 4 star maybe 5, and the city itself is wonderful. It's an old style colonial city with many buildings built in the 16th century. There are a about 30 Mayan ruins sites within an hour drive. Several haciendas which have been restored and are now 4 and 5 star resorts. The Hacienda Temozon is very nice, several US Presidents and former Presidents have stayed there.
Here's a link to more info on this area-
Yucatan Today
If you'd like more info, just ask.