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SunnyDays

ERA5 almanac — 8 years of real data

Hilton Head in January

Hilton Head in January is historically a poor month for sun: only 0% of days clear across 8 years (n=248, avg high 58°F). October is the clearest month for Hilton Head historically. Historical average, not a forecast.

What you are reading: 8-year historical averages from the ERA5 reanalysis, not a forecast. A month that is historically 90% clear can still be overcast on your specific trip. For this week’s actual forecast, see the live Hilton Head page. Both can be true at once: “historically strong in this month; this particular week is not.” We label which is which.

Early vs. Late January

Clear-sky percentage for Hilton Head in January, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early January
1st–15th		 1% n=120 58°F
Late January
16th–end		 0% n=128 58°F
Full month average 0% n=248 58°F

Sunshine & warmth in January

A second measure using actual sunshine hours (ERA5 sunshine_duration), not the daily weather code. A Lowcountry day with 12 hours of sun and a 25-minute afternoon storm is counted below as a warm, sunny day — because it was. How we define this.

Sunshine-based metrics for Hilton Head in January. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early January
1st–15th		 5% n=120
Late January
16th–end		 1% n=128
Full month average 3% n=248
9.5 h median sunshine per day 65% of days exceed 8 h sunshine 27% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 0%. Sunshine-based “warm & sunny”: 3%.

Bottom line

Hilton Head is historically almost never clear in January: only 0% of days meet the clear bar across 8 years (n=248). Come back in October if you want clear skies here. Plan entirely around indoor or overcast-friendly activities.

→ See all destinations in October — historically the best month for sun in Hilton Head.

Every month in Hilton Head

Compare across all months with data. Numbers are historical clear-sky %.

Historical clear-sky % for Hilton Head, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January ← this page 0% n=248 All destinations →
February 10% n=226 All destinations →
March 19% n=248 All destinations →
April 38% n=240 All destinations →
May 39% n=248 All destinations →
June 20% n=240 All destinations →
July 15% n=248 All destinations →
August 9% n=248 All destinations →
September 33% n=240 All destinations →
October 45% n=248 All destinations →
November 12% n=240 All destinations →
December 6% n=248 All destinations →

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.