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SunnyDays

ERA5 almanac — 8 years of real data

Martha's Vineyard in September

Martha's Vineyard in September: rain frequency data not yet backfilled for this month, 72°F average high, 27% of days historically clear (n=240, ERA5 2018–2025).

Martha's Vineyard in September is historically a poor month for sun: only 27% of days clear across 8 years (n=240, avg high 72°F). August is the clearest month for Martha's Vineyard 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 Martha's Vineyard 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 Martha's Vineyard 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		 39% n=120 72°F
Late September
16th–end		 15% n=120 72°F
Full month average 27% n=240 72°F

Bottom line

Martha's Vineyard is mostly overcast in September historically: only 27% of days are clear across 8 years (n=240), avg high 72°F. The two halves differ materially (39% early, 15% late) — favour the early half of the month. If you want sun in Martha's Vineyard, August is historically much better. Most visitors this month will see more clouds than sun.

→ See all destinations in August — historically the best month for sun in Martha's Vineyard.

Every month in Martha's Vineyard

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

Historical clear-sky % for Martha's Vineyard, 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 3% n=248 All destinations →
June 25% n=240 All destinations →
July 45% n=248 All destinations →
August 46% n=248 All destinations →
September ← this page 27% n=240 All destinations →
October 3% n=248 All destinations →
November 0% n=240 All destinations →
December 0% n=248 All destinations →

Frequently asked

Is Martha's Vineyard good for sun in September?

Not usually. Martha's Vineyard is historically overcast in September: only 27% of days are clear (avg high 72°F, n=240 days, ERA5 2018–2025). August is historically far better for sun here.

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.