ERA5 almanac comparison — 8 years of real data
Costa Rica — Guanacaste vs Sea Island: weather in May
Sea Island edges out Costa Rica — Guanacaste for sun in May: 36% clear historically versus 9% (8-year ERA5 average, a 27-point gap). Costa Rica — Guanacaste also sees measurably more rain than Sea Island this month (78% vs 36% of days). Both are viable — Sea Island is the safer bet.
What you are reading: 8-year historical averages, not a forecast.
Either destination can still surprise you this specific May. For this
week’s actual forecast, each destination links to its live page below.
Costa Rica — Guanacaste
CR
- Clear days, May
- 9%
- Sample size
- n=248 days
- Avg high
- 91°F
- Early May (1st–15th)
- 13%
- Late May (16th–end)
- 5%
- Rain frequency
- 78% of days
Sea Island
GA
- Clear days, May
- 36%
- Sample size
- n=248 days
- Avg high
- 81°F
- Early May (1st–15th)
- 41%
- Late May (16th–end)
- 31%
- Rain frequency
- 36% of days
Compare Costa Rica — Guanacaste 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.