ERA5 almanac comparison — 8 years of real data
San Antonio vs Sea Island: weather in September
Essentially a tie in September: San Antonio is 36% clear historically, Sea Island is 32% clear (8-year ERA5 average) — within the noise. Avg high 92°F vs 83°F. Sea Island also sees measurably more rain than San Antonio this month (53% vs 31% of days). Pick based on flight time or price, not weather — the weather won't decide this one for you.
San Antonio
TX
- Clear days, September
- 36%
- Sample size
- n=240 days
- Avg high
- 92°F
- Early September (1st–15th)
- 30%
- Late September (16th–end)
- 42%
- Rain frequency
- 31% of days
Sea Island
GA
- Clear days, September
- 32%
- Sample size
- n=240 days
- Avg high
- 83°F
- Early September (1st–15th)
- 26%
- Late September (16th–end)
- 37%
- Rain frequency
- 53% of days
Compare San Antonio vs Sea Island in another month
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.