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SunnyDays

ERA5 almanac — 8 years of real data

Savannah in September

Savannah in September is historically a poor month for sun: only 32% of days clear across 8 years (n=240, avg high 85°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 Savannah 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 Savannah 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		 28% n=120 85°F
Late September
16th–end		 37% n=120 85°F
Full month average 32% n=240 85°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 Savannah 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		 90% n=120
Late September
16th–end		 89% n=120
Full month average 90% n=240
11.3 h median sunshine per day 82% of days exceed 8 h sunshine 50% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 32%. Sunshine-based “warm & sunny”: 90%. The 58-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

Savannah is mostly overcast in September historically: only 32% of days are clear across 8 years (n=240), avg high 85°F. Most visitors this month will see more clouds than sun.

Every month in Savannah

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

Historical clear-sky % for Savannah, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 2% n=248 All destinations →
February 16% n=226 All destinations →
March 25% n=248 All destinations →
April 44% n=240 All destinations →
May 37% n=248 All destinations →
June 24% n=240 All destinations →
July 14% n=248 All destinations →
August 8% n=248 All destinations →
September ← this page 32% n=240 All destinations →
October 47% n=248 All destinations →
November 18% n=240 All destinations →
December 8% n=248 All destinations →

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.