Weather in Mexico City in September

A good month. September is a solid month to be in Mexico City. You should expect rain on 26 days of the month, which is more days wet than dry.

September ranks 12 of 12 — near the bottom of Mexico City's year. December is the month that works, and the swing between the two is 33 points, which is a different holiday rather than a slightly better one. Worth keeping in perspective: September is the weakest month of Mexico City's year and it is still a perfectly good one. The downside here is small.

Rain on 26 of the month's 30 days, 3 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. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: it never really gets hot: not one day in an average September reaches 30 °C. Across the twenty years measured, the hottest September day reached 26.9 °C and the coldest night fell to 3.1 °C.

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 223 mm against 78 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 148 mm average is a reasonable planning figure, not a promise.

Wind is light at 3.8 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: 23.6 °C in August, 22.7 here, 22.5 in October. Nothing about the timing within the month matters much. Rain is the thing that moves: October brings 11 days less of it, so pushing the dates later buys drier weather.

Daylight in September

12.3 hours of daylight, losing 0.5 hours across the month. That is between Mexico City's extremes of 13.3 and 11 hours, so days are long enough not to constrain the plan.

An inland climate

Despite being inland, the year stays fairly even: 21.8 °C between the year's warmest afternoons and coldest nights. At 2240 m, altitude is doing as much work here as latitude: thinner air means fierce sun by day and heat that leaves the moment it sets.

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 Mexico City versus nearby

If Mexico City is one option among several, the nearby comparison is worth making. Santiago de Querétaro is close enough to be a coin toss — 3.5 °C warmer, 7 days less rain. Morelia is close enough to be a coin toss — within a degree on temperature, 1 day less rain.

So: September is a compromise. December is 33 points better and is what Mexico City 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 Mexico City

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