Skip to main content
SunnyDays

ERA5 almanac — 8 years of real data

Mexico City in September

Mexico City in September: 84% of days see measurable rain, 73°F average high, 4% of days historically clear (n=240, ERA5 2018–2025).

Mexico City in September is historically a poor month for sun: only 4% of days clear across 8 years (n=240, avg high 73°F). February is the clearest month for Mexico City historically. Historical average, not a forecast.

What you are reading: 8-year historical averages from the ERA5 reanalysis, not a forecast. A month that is historically 90% clear can still be overcast on your specific trip. For this week’s actual forecast, see the live Mexico City page. Both can be true at once: “historically strong in this month; this particular week is not.” We label which is which.

Early vs. Late September

Clear-sky percentage for Mexico City in September, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early September
1st–15th		 2% n=120 73°F
Late September
16th–end		 6% n=120 73°F
Full month average 4% n=240 73°F

Sunshine & warmth in September

A second measure using actual sunshine hours (ERA5 sunshine_duration), not the daily weather code. A Lowcountry day with 12 hours of sun and a 25-minute afternoon storm is counted below as a warm, sunny day — because it was. How we define this.

Sunshine-based metrics for Mexico City in September. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early September
1st–15th		 62% n=120
Late September
16th–end		 51% n=120
Full month average 56% n=240
10.5 h median sunshine per day 90% of days exceed 8 h sunshine 84% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 4%. Sunshine-based “warm & sunny”: 56%. The 52-point gap is from brief afternoon convective storms that stamp the whole day as “rain” in the WMO code but leave the bulk of the sunshine untouched.

Bottom line

Mexico City is historically almost never clear in September: only 4% of days meet the clear bar across 8 years (n=240). Come back in February if you want clear skies here. Plan entirely around indoor or overcast-friendly activities.

→ See all destinations in February — historically the best month for sun in Mexico City.

Every month in Mexico City

Compare across all months with data. Numbers are historical clear-sky %.

Historical clear-sky % for Mexico City, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 52% n=248 All destinations →
February 71% n=226 All destinations →
March 71% n=248 All destinations →
April 51% n=240 All destinations →
May 33% n=248 All destinations →
June 18% n=240 All destinations →
July 1% n=248 All destinations →
August 2% n=248 All destinations →
September ← this page 4% n=240 All destinations →
October 20% n=248 All destinations →
November 52% n=240 All destinations →
December 50% n=248 All destinations →

Frequently asked

Does it rain in Mexico City in September?

Yes, frequently. In Mexico City, 84% of days in September see measurable rain, based on 8 years of ERA5 historical data (n=240 days, 2018–2025). This is a historical average, not a forecast.

Is Mexico City good for sun in September?

Not usually. Mexico City is historically overcast in September: only 4% of days are clear (avg high 73°F, n=240 days, ERA5 2018–2025). February is historically far better for sun here.

All percentages are historical averages from the ERA5 reanalysis via Open-Meteo, 8 full years (2018–2025). “Clear” means avg high ≥ 72 °F, precipitation < 1 mm, and a non-precipitation weather code. This is history, not a forecast. The live 7-day outlook for any destination is on its own page and may differ from the long-run average. Data from Open-Meteo.