ERA5 almanac — 8 years of real data

The Hamptons in September

The Hamptons in September: 33% of days see measurable rain, 72°F average high, 28% of days historically clear (n=240, ERA5 2018–2025).

The Hamptons in September is historically a poor month for sun: only 28% of days clear across 8 years (n=240, avg high 72°F). July is the clearest month for The Hamptons 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 The Hamptons 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 The Hamptons 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	72°F
Late September 16th–end	17%	n=120	72°F
Full month average	28%	n=240	72°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 The Hamptons 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	62%	n=120
Late September 16th–end	28%	n=120
Full month average	45%	n=240

11.3 h median sunshine per day 76% of days exceed 8 h sunshine 33% of days see ≥ 1 mm rain — rain is not hidden

Comparison (old vs new): WMO-code “clear” bar: 28%. Sunshine-based “warm & sunny”: 45%. The 17-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

The Hamptons is mostly overcast in September historically: only 28% of days are clear across 8 years (n=240), avg high 72°F. The two halves differ materially (38% early, 17% late) — favour the early half of the month. If you want sun in The Hamptons, July is historically much better. Most visitors this month will see more clouds than sun.

→ See all destinations in July — historically the best month for sun in The Hamptons.

Every month in The Hamptons

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

Historical clear-sky % for The Hamptons, 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	22%	n=240	All destinations →
July	44%	n=248	All destinations →
August	44%	n=248	All destinations →
September ← this page	28%	n=240	All destinations →
October	3%	n=248	All destinations →
November	0%	n=240	All destinations →
December	0%	n=248	All destinations →

Frequently asked

Does it rain in The Hamptons in September?

Sometimes. The Hamptons sees measurable rain on 33% of days in September historically (n=240 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is The Hamptons good for sun in September?

Not usually. The Hamptons is historically overcast in September: only 28% of days are clear (avg high 72°F, n=240 days, ERA5 2018–2025). July is historically far better for sun here.

How The Hamptons compares in September

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

→ The Hamptons vs New Orleans in September — New Orleans is 28% clear historically
→ The Hamptons vs Traverse City in September — Traverse City is 28% clear historically
→ The Hamptons vs Cape Cod in September — Cape Cod is 27% clear historically

→ The Hamptons live forecast — this week’s actual 7-day weather, not historical
→ Best destinations in September — all destinations ranked by September clear-sky %
→ All destinations
→ Raw data (JSON) — buckets, n, source

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.