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SunnyDays

ERA5 almanac — 8 years of real data

Barcelona in September

Barcelona in September: 36% of days see measurable rain, 78°F average high, 38% of days historically clear (n=240, ERA5 2018–2025).

Barcelona in September is historically a poor month for sun: only 38% of days clear across 8 years (n=240, avg high 78°F). 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 Barcelona 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 Barcelona 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		 38% n=120 78°F
Late September
16th–end		 37% n=120 78°F
Full month average 38% n=240 78°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 Barcelona 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		 88% n=120
Late September
16th–end		 83% n=120
Full month average 86% n=240
11.4 h median sunshine per day 86% of days exceed 8 h sunshine 36% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 38%. Sunshine-based “warm & sunny”: 86%. The 48-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

Barcelona is mostly overcast in September historically: only 38% of days are clear across 8 years (n=240), avg high 78°F. Most visitors this month will see more clouds than sun.

Every month in Barcelona

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

Historical clear-sky % for Barcelona, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 0% n=226 All destinations →
March 3% n=248 All destinations →
April 4% n=240 All destinations →
May 25% n=248 All destinations →
June 61% n=240 All destinations →
July 64% n=248 All destinations →
August 53% n=248 All destinations →
September ← this page 38% n=240 All destinations →
October 27% n=248 All destinations →
November 4% n=240 All destinations →
December 0% n=248 All destinations →

Frequently asked

Does it rain in Barcelona in September?

Sometimes. Barcelona sees measurable rain on 36% of days in September historically (n=240 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Barcelona good for sun in September?

It's mixed. Barcelona in September is clear on 38% of days historically (avg high 78°F, n=240 days, ERA5 2018–2025) — the outcome varies year to year.

How Barcelona compares in September

Head-to-head clear-sky comparisons against destinations travelers plausibly weigh against Barcelona this month — same passport tier, similar flight distance, both sides from the same 8-year ERA5 record.

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.