ERA5 almanac — 8 years of real data

Puerto Rico in May

Puerto Rico in May: rain frequency data not yet backfilled for this month, 87°F average high, 7% of days historically clear (n=248, ERA5 2018–2025).

Puerto Rico in May is historically a poor month for sun: only 7% of days clear across 8 years (n=248, avg high 87°F). January is the clearest month for Puerto Rico 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 Puerto Rico 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 Puerto Rico 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	8%	n=120	87°F
Late May 16th–end	7%	n=128	87°F
Full month average	7%	n=248	87°F

Bottom line

Puerto Rico is a poor choice for sun in May: just 7% of days clear historically (n=248). January is the historically strongest month for sun here. The 8-year record is consistent — this is not a fluke bad stretch.

→ See all destinations in January — historically the best month for sun in Puerto Rico.

Every month in Puerto Rico

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

Historical clear-sky % for Puerto Rico, all months, ERA5 2018–2025.
Month	% Clear	Sample (n)
January	15%	n=248	All destinations →
February	15%	n=226	All destinations →
March	15%	n=248	All destinations →
April	10%	n=240	All destinations →
May ← this page	7%	n=248	All destinations →
June	15%	n=240	All destinations →
July	9%	n=248	All destinations →
August	8%	n=248	All destinations →
September	4%	n=240	All destinations →
October	9%	n=248	All destinations →
November	11%	n=240	All destinations →
December	14%	n=248	All destinations →

Frequently asked

Is Puerto Rico good for sun in May?

Not usually. Puerto Rico is historically overcast in May: only 7% of days are clear (avg high 87°F, n=248 days, ERA5 2018–2025). January is historically far better for sun here.

→ Puerto Rico live forecast — this week’s actual 7-day weather, not historical
→ Best destinations in May — all destinations ranked by May 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.