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SunnyDays

ERA5 almanac comparison — 8 years of real data

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

Costa Rica — Guanacaste is the clear winner for sun in January: 79% of days historically clear versus just 18% in St. John, USVI — a 61-point gap across 8 years of ERA5 data. St. John, USVI also sees measurably more rain than Costa Rica — Guanacaste this month (44% vs 6% 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 January. For this week’s actual forecast, each destination links to its live page below.

Costa Rica — Guanacaste

CR

Clear days, January
79%
Sample size
n=248 days
Avg high
91°F
Early January (1st–15th)
72%
Late January (16th–end)
85%
Rain frequency
6% of days

St. John, USVI

VI

Clear days, January
18%
Sample size
n=248 days
Avg high
75°F
Early January (1st–15th)
18%
Late January (16th–end)
18%
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.