Averages for Cancun in July. Weather lowdown. July is one of the hottest months of the year for Cancun, Mexico. And even though it falls within hurricane season, hurricanes are most likely to hit the resort between August and November, which makes July a safe month to visit.uring this month, the average temperature for Cancun is the same as it is in June – 28°C/82°F created by average highs of 33°C/91°F during the heat of the day and average lows of 25°C/77°F in the coolest part of the night. Daily averages fluctuate between 28°C/82°F and 29°C/84°C for the entire month.