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SunnyDays

ERA5 almanac — 8 years of real data

Sea Island in March

Sea Island in March is historically a poor month for sun: only 15% of days clear across 8 years (n=248, avg high 69°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 March

Clear-sky percentage for Sea Island in March, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early March
1st–15th		 12% n=120 69°F
Late March
16th–end		 17% n=128 69°F
Full month average 15% n=248 69°F

Sunshine & warmth in March

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 March. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early March
1st–15th		 23% n=120
Late March
16th–end		 32% n=128
Full month average 28% n=248
11.0 h median sunshine per day 77% of days exceed 8 h sunshine 29% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 15%. Sunshine-based “warm & sunny”: 28%. The 13-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 March: just 15% 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 ← this page 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 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.