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SunnyDays

ERA5 almanac — 8 years of real data

Miami in September

Miami in September is historically a poor month for sun: only 4% of days clear across 8 years (n=240, avg high 86°F). March is the clearest month for Miami 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 Miami 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 Miami 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		 5% n=120 86°F
Late September
16th–end		 4% n=120 86°F
Full month average 4% n=240 86°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 Miami 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		 92% n=120
Late September
16th–end		 88% n=120
Full month average 90% n=240
11.2 h median sunshine per day 79% of days exceed 8 h sunshine 80% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 4%. Sunshine-based “warm & sunny”: 90%. The 86-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

Miami is historically almost never clear in September: only 4% of days meet the clear bar across 8 years (n=240). Come back in March if you want clear skies here. Plan entirely around indoor or overcast-friendly activities.

→ See all destinations in March — historically the best month for sun in Miami.

Every month in Miami

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

Historical clear-sky % for Miami, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 28% n=248 All destinations →
February 26% n=226 All destinations →
March 32% n=248 All destinations →
April 27% n=240 All destinations →
May 20% n=248 All destinations →
June 2% n=240 All destinations →
July 6% n=248 All destinations →
August 2% n=248 All destinations →
September ← this page 4% n=240 All destinations →
October 11% n=248 All destinations →
November 25% n=240 All destinations →
December 28% 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.