It generally storms inland every afternoon as the heat rises in the warm air and forms thunderstorm clouds. Out on the Hotel Zone island, if it rains at all, it's a short period of time. One of my most memorable "moments" on a Cancun/Riviera Maya vacation occurred when my wife and I made love on our balcony at the Riu Palace Rivera Maya in a heavy, warm rain. Don't think an afternoon rain is a bad thing! Don't underestimate
There is a possible storm developing, as yet unnanmed, but all the tracking forecasts have it heading to the North East side of Cuba towards Florida. If the tracking is correct it wont have any impact in Cancun.