Skip to main content
SunnyDays

ERA5 almanac — 8 years of real data

Hilton Head in April

Hilton Head in April is historically a poor month for sun: only 38% of days clear across 8 years (n=240, avg high 74°F). 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 April

Clear-sky percentage for Hilton Head in April, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early April
1st–15th		 31% n=120 74°F
Late April
16th–end		 44% n=120 74°F
Full month average 38% n=240 74°F

Sunshine & warmth in April

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 April. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early April
1st–15th		 60% n=120
Late April
16th–end		 76% n=120
Full month average 68% n=240
12.3 h median sunshine per day 86% of days exceed 8 h sunshine 28% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 38%. Sunshine-based “warm & sunny”: 68%. 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 is mostly overcast in April historically: only 38% of days are clear across 8 years (n=240), avg high 74°F. Most visitors this month will see more clouds than 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 ← this page 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.