I just looked at the average temps for the month of July... Lows 78, high 90. The 90 is not that hard to deal with if you're near the water or a water park, zip lines, etc. But 78 for a nite time low, better make sure you have accommodations with AC , or you might die there in Cancun! Have a good time Lawrence. I've taken my family to Mexico a couple times, Cabo, La Paz, but never Cancun, maybe someday.