ERA5 almanac comparison — 8 years of real data
Costa Rica — Guanacaste vs St. Barthélemy: weather in December
Costa Rica — Guanacaste is the clear winner for sun in December: 62% of days historically clear versus just 18% in St. Barthélemy — a 44-point gap across 8 years of ERA5 data. St. Barthélemy also sees measurably more rain than Costa Rica — Guanacaste this month (41% vs 15% of days). This isn't close.
Costa Rica — Guanacaste
CR
- Clear days, December
- 62%
- Sample size
- n=248 days
- Avg high
- 89°F
- Early December (1st–15th)
- 64%
- Late December (16th–end)
- 61%
- Rain frequency
- 15% of days
St. Barthélemy
BL
- Clear days, December
- 18%
- Sample size
- n=248 days
- Avg high
- 80°F
- Early December (1st–15th)
- 10%
- Late December (16th–end)
- 25%
- Rain frequency
- 41% of days
Compare Costa Rica — Guanacaste 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.