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SunnyDays

ERA5 almanac comparison — 8 years of real data

Costa Rica — Guanacaste vs Hilton Head: weather in September

Hilton Head is the clear winner for sun in September: 33% of days historically clear versus just 2% in Costa Rica — Guanacaste — a 31-point gap across 8 years of ERA5 data. Costa Rica — Guanacaste also sees measurably more rain than Hilton Head this month (92% vs 50% 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 September. For this week’s actual forecast, each destination links to its live page below.

Costa Rica — Guanacaste

CR

Clear days, September
2%
Sample size
n=240 days
Avg high
88°F
Early September (1st–15th)
3%
Late September (16th–end)
2%
Rain frequency
92% of days

Hilton Head

SC

Clear days, September
33%
Sample size
n=240 days
Avg high
83°F
Early September (1st–15th)
28%
Late September (16th–end)
38%
Rain frequency
50% of days
See this week’s live forecast →

Compare Costa Rica — Guanacaste vs Hilton Head 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.