Weather in Cancún in September

Shoulder season. September is shoulder season in Cancún — cheaper, quieter, and a genuine gamble. You should expect rain on 24 days of the month, which is more days wet than dry.

September ranks 11 of 12 — near the bottom of Cancún's year. February is the month that works, and the swing between the two is 36 points, which is a different holiday rather than a slightly better one.

Rain on 24 of the month's 30 days, 5 of them heavy. At that frequency a wet-weather backup is not a contingency, it is the itinerary — book the indoor things first and treat the clear days as the bonus. Natural fibres and a second shirt for the day. At 82% nothing dries, including you.

What the averages hide

Averages flatten a month, and this one hides a few things: 14 days top 30 °C — hot spells arrive, but they break; the day barely swings — 3.5 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 33.4 °C and the coldest night fell to 23.9 °C, and the wettest single day dropped 50 mm — roughly 30% of the month's rain in one day.

September is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest September on record still delivered 358 mm against 94 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 166 mm average is a reasonable planning figure, not a promise.

Wind is light at 7 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 82%, high enough to notice on the warm days without dominating them.

How September sits in the year

Temperatures hold steady either side: 30.5 °C in August, 30 here, 28.8 in October. Nothing about the timing within the month matters much.

Daylight in September

12.3 hours of daylight, losing 0.6 hours across the month. That is between Cancún's extremes of 13.4 and 10.9 hours, so days are long enough not to constrain the plan.

Sea temperature

The sea sits at about 28.9 °C in September — warm enough that the water offers no relief from the heat. This is the warmest the water gets all year.

How busy it gets

Off season. The genuine off season: cheapest by a distance, with the caveat that some tours and restaurants close entirely.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

September in Cancún versus nearby

If Cancún is one option among several, the nearby comparison is worth making. Mérida is close enough to be a coin toss — within a degree on temperature, 1 day less rain. Key West is close enough to be a coin toss — within a degree on temperature, 1 day less rain.

So: September is a compromise. February is 35 points better and is what Cancún is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Cancún

See all twelve months in Cancún, or where else to go in September.