The weather in Cancun changes quickly and constantly. The forecast usually says rains, but that can mean our normal 5 minute afternoon shower or more rarely a full day of rain. It rains here at night more often than during the day. Because we are right on the coast, systems move in quickly and out even faster. Be prepared for sun, showers and humid weather all in the same day!
Weather conditions do not stop most tours. Sightseeing tours like Chichen Itza, Tulum & Coba are a distance from Cancun and the weather there will be different. Not necessarily a bad thing to have shower during a hot day at the ruins. If it is windy or stormy the port authority may close the port and water tours like the Jungle tour or boat tours will not run. You will have the chance to reschedule or get a refund if the tour operator cancels the tour. Otherwise its a Go!
Fahrenheit on the left and Celsius forecasts below.