Skip to main content
SunnyDays

ERA5 almanac — 8 years of real data

Sea Island in October

Sea Island in October is a mixed month for sun: 42% 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 Sea Island 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 Sea Island 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		 40% n=120 77°F
Late October
16th–end		 44% n=128 77°F
Full month average 42% 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 Sea Island 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		 82% n=120
Late October
16th–end		 75% n=128
Full month average 78% n=248
10.7 h median sunshine per day 82% of days exceed 8 h sunshine 30% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 42%. Sunshine-based “warm & sunny”: 78%. The 36-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

Sea Island in October is genuinely mixed: 42% of days historically clear (n=248), avg high 77°F — more cloudy than clear. The outcome varies year to year; don't book if you need guaranteed sun.

Every month in Sea Island

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

Historical clear-sky % for Sea Island, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 2% n=248 All destinations →
February 8% n=226 All destinations →
March 15% n=248 All destinations →
April 36% n=240 All destinations →
May 36% n=248 All destinations →
June 24% n=240 All destinations →
July 14% n=248 All destinations →
August 7% n=248 All destinations →
September 32% n=240 All destinations →
October ← this page 42% n=248 All destinations →
November 17% n=240 All destinations →
December 7% 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.