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SunnyDays

ERA5 almanac — 8 years of real data

Rome in September

Rome in September: 29% of days see measurable rain, 82°F average high, 50% of days historically clear (n=240, ERA5 2018–2025).

Rome in September is a mixed month for sun: 50% of days historically clear (n=240, avg high 82°F). The outcome varies year to year — check the early/late split below. 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 Rome 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 Rome 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		 61% n=120 82°F
Late September
16th–end		 38% n=120 82°F
Full month average 50% n=240 82°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 Rome 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		 95% n=120
Late September
16th–end		 90% n=120
Full month average 92% n=240
11.8 h median sunshine per day 93% of days exceed 8 h sunshine 29% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 50%. Sunshine-based “warm & sunny”: 92%. The 42-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

Rome in September is genuinely mixed: 50% of days historically clear (n=240), avg high 82°F — roughly even odds. The two halves differ materially (61% early, 38% late) — favour the early half of the month. The outcome varies year to year; don't book if you need guaranteed sun.

Every month in Rome

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

Historical clear-sky % for Rome, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 0% n=226 All destinations →
March 2% n=248 All destinations →
April 16% n=240 All destinations →
May 30% n=248 All destinations →
June 65% n=240 All destinations →
July 77% n=248 All destinations →
August 59% n=248 All destinations →
September ← this page 50% n=240 All destinations →
October 38% n=248 All destinations →
November 2% n=240 All destinations →
December 0% n=248 All destinations →

Frequently asked

Does it rain in Rome in September?

Sometimes. Rome sees measurable rain on 29% of days in September historically (n=240 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Rome good for sun in September?

It's mixed. Rome in September is clear on 50% of days historically (avg high 82°F, n=240 days, ERA5 2018–2025) — the outcome varies year to year.

How Rome compares in September

Head-to-head clear-sky comparisons against destinations travelers plausibly weigh against Rome 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.