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SunnyDays

ERA5 almanac — 8 years of real data

Outer Banks in September

Outer Banks in September is a mixed month for sun: 40% of days historically clear (n=240, avg high 78°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 Outer Banks 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 September

Clear-sky percentage for Outer Banks in September, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early September
1st–15th		 38% n=120 78°F
Late September
16th–end		 43% n=120 78°F
Full month average 40% n=240 78°F

Sunshine & warmth in September

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 Outer Banks in September. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early September
1st–15th		 88% n=120
Late September
16th–end		 81% n=120
Full month average 84% n=240
11.8 h median sunshine per day 82% of days exceed 8 h sunshine 36% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 40%. Sunshine-based “warm & sunny”: 84%. The 44-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

Outer Banks in September is genuinely mixed: 40% of days historically clear (n=240), avg high 78°F — more cloudy than clear. The outcome varies year to year; don't book if you need guaranteed sun.

Every month in Outer Banks

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

Historical clear-sky % for Outer Banks, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 0% n=226 All destinations →
March 0% n=248 All destinations →
April 1% n=240 All destinations →
May 16% n=248 All destinations →
June 47% n=240 All destinations →
July 35% n=248 All destinations →
August 35% n=248 All destinations →
September ← this page 40% n=240 All destinations →
October 20% n=248 All destinations →
November 1% n=240 All destinations →
December 0% 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.