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SunnyDays

ERA5 almanac — 8 years of real data

Hilton Head in October

Hilton Head in October is a mixed month for sun: 45% of days historically clear (n=248, avg high 77°F). The outcome varies year to year — check the early/late split below. 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 October

Clear-sky percentage for Hilton Head in October, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early October
1st–15th		 49% n=120 77°F
Late October
16th–end		 41% n=128 77°F
Full month average 45% n=248 77°F

Sunshine & warmth in October

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 October. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early October
1st–15th		 81% n=120
Late October
16th–end		 70% n=128
Full month average 75% n=248
10.7 h median sunshine per day 82% of days exceed 8 h sunshine 24% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 45%. Sunshine-based “warm & sunny”: 75%. The 30-point gap is from brief afternoon convective storms that stamp the whole day as “rain” in the WMO code but leave the bulk of the sunshine untouched.

Bottom line

Hilton Head in October is genuinely mixed: 45% of days historically clear (n=248), avg high 77°F — roughly even odds. The outcome varies year to year; don't book if you need guaranteed sun.

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 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 ← this page 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.