I learned not to worry about the weather even if it says rain we saw very little while we were there last year but it was forecast everyday. Plan for VERY HOT weather and bring plenty of sunscreen, more than you normally would and reapply every hour or so. We had a blast.
We went last week of August last year and the weather was phenomenal! I would rather be in Cancun in August than in January for example.
august we was at TTR in august 2013 really hot clear blue skies lovely only 1 half day of rain which was quite nice to be honest spent it at the bar by the quiet pool getting to know some people hope this helps