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SunnyDays

ERA5 almanac — 8 years of real data

Mérida in September

Mérida in September: 60% of days see measurable rain, 92°F average high, 8% of days historically clear (n=240, ERA5 2018–2025).

Mérida in September is historically a poor month for sun: only 8% of days clear across 8 years (n=240, avg high 92°F). March is the clearest month for Mérida 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 Mérida 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 Mérida 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		 8% n=120 92°F
Late September
16th–end		 9% n=120 92°F
Full month average 8% n=240 92°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 Mérida 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		 97% n=120
Late September
16th–end		 99% n=120
Full month average 98% n=240
11.5 h median sunshine per day 95% of days exceed 8 h sunshine 60% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 8%. Sunshine-based “warm & sunny”: 98%. The 90-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

Mérida is a poor choice for sun in September: just 8% of days clear historically (n=240). March is the historically strongest month for sun here. The 8-year record is consistent — this is not a fluke bad stretch.

→ See all destinations in March — historically the best month for sun in Mérida.

Every month in Mérida

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

Historical clear-sky % for Mérida, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 55% n=248 All destinations →
February 61% n=226 All destinations →
March 74% n=248 All destinations →
April 68% n=240 All destinations →
May 47% n=248 All destinations →
June 20% n=240 All destinations →
July 20% n=248 All destinations →
August 13% n=248 All destinations →
September ← this page 8% n=240 All destinations →
October 20% n=248 All destinations →
November 38% n=240 All destinations →
December 53% n=248 All destinations →

Frequently asked

Does it rain in Mérida in September?

Yes, frequently. In Mérida, 60% 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 Mérida good for sun in September?

Not usually. Mérida is historically overcast in September: only 8% of days are clear (avg high 92°F, n=240 days, ERA5 2018–2025). March 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.