ERA5 almanac comparison — 8 years of real data
Cancún vs St. Barthélemy: weather in September
St. Barthélemy edges out Cancún for sun in September: 13% clear historically versus 5% (8-year ERA5 average, a 8-point gap). Cancún also sees measurably more rain than St. Barthélemy this month (71% vs 56% of days). Both are viable — St. Barthélemy is the safer bet.
What you are reading: 8-year historical averages, not a forecast.
Either destination can still surprise you this specific September. For this
week’s actual forecast, each destination links to its live page below.
Cancún
MX
- Clear days, September
- 5%
- Sample size
- n=240 days
- Avg high
- 88°F
- Early September (1st–15th)
- 5%
- Late September (16th–end)
- 5%
- Rain frequency
- 71% of days
St. Barthélemy
BL
- Clear days, September
- 13%
- Sample size
- n=240 days
- Avg high
- 84°F
- Early September (1st–15th)
- 14%
- Late September (16th–end)
- 12%
- Rain frequency
- 56% of days
Compare Cancún vs St. Barthélemy 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.