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SunnyDays

ERA5 almanac comparison — 8 years of real data

Costa Rica — Guanacaste vs St. John, USVI: weather in December

Costa Rica — Guanacaste is the clear winner for sun in December: 62% of days historically clear versus just 16% in St. John, USVI — a 46-point gap across 8 years of ERA5 data. St. John, USVI also sees measurably more rain than Costa Rica — Guanacaste this month (44% vs 15% of days). This isn't close.

What you are reading: 8-year historical averages, not a forecast. Either destination can still surprise you this specific December. For this week’s actual forecast, each destination links to its live page below.

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. John, USVI

VI

Clear days, December
16%
Sample size
n=248 days
Avg high
76°F
Early December (1st–15th)
12%
Late December (16th–end)
20%
Rain frequency
44% 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.