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SunnyDays

ERA5 almanac — 8 years of real data

St. Barthélemy in May

St. Barthélemy in May: 32% of days see measurable rain, 81°F average high, 21% of days historically clear (n=248, ERA5 2018–2025).

St. Barthélemy in May is historically a poor month for sun: only 21% of days clear across 8 years (n=248, avg high 81°F). March is the clearest month for St. Barthélemy 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 St. Barthélemy 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 St. Barthélemy 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		 18% n=120 81°F
Late May
16th–end		 24% n=128 81°F
Full month average 21% n=248 81°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 St. Barthélemy 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		 99% n=120
Late May
16th–end		 98% n=128
Full month average 98% n=248
12.1 h median sunshine per day 96% of days exceed 8 h sunshine 32% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 21%. Sunshine-based “warm & sunny”: 98%. The 77-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

St. Barthélemy is mostly overcast in May historically: only 21% of days are clear across 8 years (n=248), avg high 81°F. If you want sun in St. Barthélemy, March is historically much better. Most visitors this month will see more clouds than sun.

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

Every month in St. Barthélemy

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

Historical clear-sky % for St. Barthélemy, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 18% n=248 All destinations →
February 12% n=226 All destinations →
March 29% n=248 All destinations →
April 22% n=240 All destinations →
May ← this page 21% n=248 All destinations →
June 19% n=240 All destinations →
July 10% n=248 All destinations →
August 14% n=248 All destinations →
September 13% n=240 All destinations →
October 20% n=248 All destinations →
November 19% n=240 All destinations →
December 18% n=248 All destinations →

Frequently asked

Does it rain in St. Barthélemy in May?

Sometimes. St. Barthélemy sees measurable rain on 32% of days in May historically (n=248 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is St. Barthélemy good for sun in May?

Not usually. St. Barthélemy is historically overcast in May: only 21% of days are clear (avg high 81°F, n=248 days, ERA5 2018–2025). March is historically far better for sun here.

How St. Barthélemy compares in May

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

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.