Skip to main content
SunnyDays

ERA5 almanac — 8 years of real data

Nantucket in August

Nantucket in August: 26% of days see measurable rain, 72°F average high, 32% of days historically clear (n=248, ERA5 2018–2025).

Nantucket in August is historically a poor month for sun: only 32% of days clear across 8 years (n=248, avg high 72°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 Nantucket 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 Nantucket 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		 37% n=120 72°F
Late August
16th–end		 27% n=128 72°F
Full month average 32% n=248 72°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 Nantucket 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		 63% n=120
Late August
16th–end		 46% n=128
Full month average 54% n=248
12.6 h median sunshine per day 86% of days exceed 8 h sunshine 26% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 32%. Sunshine-based “warm & sunny”: 54%. The 22-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

Nantucket is mostly overcast in August historically: only 32% of days are clear across 8 years (n=248), avg high 72°F. Most visitors this month will see more clouds than sun.

Every month in Nantucket

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

Historical clear-sky % for Nantucket, 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 0% n=240 All destinations →
May 0% n=248 All destinations →
June 0% n=240 All destinations →
July 24% n=248 All destinations →
August ← this page 32% n=248 All destinations →
September 6% n=240 All destinations →
October 0% n=248 All destinations →
November 0% n=240 All destinations →
December 0% n=248 All destinations →

Frequently asked

Does it rain in Nantucket in August?

Sometimes. Nantucket sees measurable rain on 26% of days in August historically (n=248 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Nantucket good for sun in August?

It's mixed. Nantucket in August is clear on 32% of days historically (avg high 72°F, n=248 days, ERA5 2018–2025) — the outcome varies year to year.

How Nantucket compares in August

Head-to-head clear-sky comparisons against destinations travelers plausibly weigh against Nantucket this month — same passport tier, similar flight distance, both sides from the same 8-year ERA5 record.

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.