ERA5 almanac — 8 years of real data

New York City in September

New York City in September: rain frequency data not yet backfilled for this month, 76°F average high, 40% of days historically clear (n=240, ERA5 2018–2025).

New York City in September is a mixed month for sun: 40% of days historically clear (n=240, avg high 76°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 New York City 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 New York City 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	41%	n=120	76°F
Late September 16th–end	38%	n=120	76°F
Full month average	40%	n=240	76°F

Bottom line

New York City in September is genuinely mixed: 40% of days historically clear (n=240), avg high 76°F — more cloudy than clear. The outcome varies year to year; don't book if you need guaranteed sun.

Every month in New York City

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

Historical clear-sky % for New York City, 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	6%	n=240	All destinations →
May	24%	n=248	All destinations →
June	39%	n=240	All destinations →
July	31%	n=248	All destinations →
August	35%	n=248	All destinations →
September ← this page	40%	n=240	All destinations →
October	13%	n=248	All destinations →
November	2%	n=240	All destinations →
December	0%	n=248	All destinations →

Frequently asked

Is New York City good for sun in September?

It's mixed. New York City in September is clear on 40% of days historically (avg high 76°F, n=240 days, ERA5 2018–2025) — the outcome varies year to year.

→ New York City 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.