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SunnyDays

ERA5 almanac — 8 years of real data

Key West in May

Key West in May is historically a poor month for sun: only 33% of days clear across 8 years (n=248, avg high 82°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 Key West 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 May

Clear-sky percentage for Key West in May, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early May
1st–15th		 38% n=120 82°F
Late May
16th–end		 29% n=128 82°F
Full month average 33% n=248 82°F

Sunshine & warmth in May

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 Key West in May. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early May
1st–15th		 97% n=120
Late May
16th–end		 93% n=128
Full month average 95% n=248
13.0 h median sunshine per day 93% of days exceed 8 h sunshine 38% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 33%. Sunshine-based “warm & sunny”: 95%. The 62-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

Key West is mostly overcast in May historically: only 33% of days are clear across 8 years (n=248), avg high 82°F. Most visitors this month will see more clouds than sun.

Every month in Key West

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

Historical clear-sky % for Key West, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 27% n=248 All destinations →
February 37% n=226 All destinations →
March 45% n=248 All destinations →
April 44% n=240 All destinations →
May ← this page 33% n=248 All destinations →
June 14% n=240 All destinations →
July 17% n=248 All destinations →
August 13% n=248 All destinations →
September 11% n=240 All destinations →
October 13% n=248 All destinations →
November 30% n=240 All destinations →
December 41% 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.