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SunnyDays

ERA5 almanac — 8 years of real data

Sea Island in August

Sea Island in August is historically a poor month for sun: only 7% of days clear across 8 years (n=248, avg high 85°F). October is the clearest month for Sea Island 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 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 August

Clear-sky percentage for Sea Island in August, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early August
1st–15th		 6% n=120 85°F
Late August
16th–end		 8% n=128 85°F
Full month average 7% n=248 85°F

Sunshine & warmth in August

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 August. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early August
1st–15th		 95% n=120
Late August
16th–end		 92% n=128
Full month average 93% n=248
12.0 h median sunshine per day 86% of days exceed 8 h sunshine 66% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 7%. Sunshine-based “warm & sunny”: 93%. The 86-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 is a poor choice for sun in August: just 7% of days clear historically (n=248). October is the historically strongest month for sun here. The 8-year record is consistent — this is not a fluke bad stretch.

→ See all destinations in October — historically the best month for sun in Sea Island.

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 ← this page 7% n=248 All destinations →
September 32% n=240 All destinations →
October 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.