ERA5 almanac comparison — 8 years of real data
Costa Rica — Guanacaste vs St. John, USVI: weather in May
St. John, USVI edges out Costa Rica — Guanacaste for sun in May: 25% clear historically versus 9% (8-year ERA5 average, a 16-point gap). Costa Rica — Guanacaste also sees measurably more rain than St. John, USVI this month (78% vs 41% of days). Both are viable — St. John, USVI is the safer bet.
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
St. John, USVI
VI
- Clear days, May
- 25%
- Sample size
- n=248 days
- Avg high
- 78°F
- Early May (1st–15th)
- 23%
- Late May (16th–end)
- 27%
- Rain frequency
- 41% of days
Compare Costa Rica — Guanacaste vs St. John, USVI 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.