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SunnyDays

ERA5 almanac — 8 years of real data

Atlanta in September

Atlanta in September: 34% of days see measurable rain, 83°F average high, 40% of days historically clear (n=240, ERA5 2018–2025).

Atlanta in September is a mixed month for sun: 40% of days historically clear (n=240, avg high 83°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 Atlanta 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 Atlanta 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 83°F
Late September
16th–end		 42% n=120 83°F
Full month average 40% n=240 83°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 Atlanta 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		 91% n=120
Late September
16th–end		 83% n=120
Full month average 87% n=240
11.4 h median sunshine per day 81% of days exceed 8 h sunshine 34% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 40%. Sunshine-based “warm & sunny”: 87%. The 47-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

Atlanta in September is genuinely mixed: 40% of days historically clear (n=240), avg high 83°F — more cloudy than clear. The outcome varies year to year; don't book if you need guaranteed sun.

Every month in Atlanta

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

Historical clear-sky % for Atlanta, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 2% n=226 All destinations →
March 11% n=248 All destinations →
April 24% n=240 All destinations →
May 32% n=248 All destinations →
June 26% n=240 All destinations →
July 15% n=248 All destinations →
August 20% n=248 All destinations →
September ← this page 40% n=240 All destinations →
October 34% n=248 All destinations →
November 6% n=240 All destinations →
December 1% n=248 All destinations →

Frequently asked

Does it rain in Atlanta in September?

Sometimes. Atlanta sees measurable rain on 34% of days in September historically (n=240 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Atlanta good for sun in September?

It's mixed. Atlanta in September is clear on 40% of days historically (avg high 83°F, n=240 days, ERA5 2018–2025) — the outcome varies year to year.

How Atlanta compares in September

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