ERA5 almanac comparison — 8 years of real data
Costa Rica — Guanacaste vs Key West: weather in May
Key West edges out Costa Rica — Guanacaste for sun in May: 33% clear historically versus 9% (8-year ERA5 average, a 24-point gap). Costa Rica — Guanacaste also sees measurably more rain than Key West this month (78% vs 38% of days). Both are viable — Key West 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
Key West
FL
- Clear days, May
- 33%
- Sample size
- n=248 days
- Avg high
- 82°F
- Early May (1st–15th)
- 38%
- Late May (16th–end)
- 29%
- Rain frequency
- 38% of days
Compare Costa Rica — Guanacaste vs Key West 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.