ERA5 almanac — 8 years of real data

Costa Rica — Guanacaste in March

Costa Rica — Guanacaste in March: 10% of days see measurable rain, 96°F average high, 70% of days historically clear (n=248, ERA5 2018–2025).

Historically one of the better months to visit Costa Rica — Guanacaste for sun: 70% of days are clear on average (n=248, avg high 96°F). Every percentage here is a historical average from 8 years of ERA5 data — 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 Costa Rica — Guanacaste 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 March

Clear-sky percentage for Costa Rica — Guanacaste in March, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period	% Clear days	Sample (n)	Avg high
Early March 1st–15th	77%	n=120	96°F
Late March 16th–end	63%	n=128	96°F
Full month average	70%	n=248	96°F

Sunshine & warmth in March

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 Costa Rica — Guanacaste in March. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period	Warm & sunny (≥72°F, >6 h sun)	Sample (n)
Early March 1st–15th	100%	n=120
Late March 16th–end	100%	n=128
Full month average	100%	n=248

11.8 h median sunshine per day 99% of days exceed 8 h sunshine 10% of days see ≥ 1 mm rain — rain is not hidden

Comparison (old vs new): WMO-code “clear” bar: 70%. Sunshine-based “warm & sunny”: 100%. The 30-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

Costa Rica — Guanacaste clears solidly in March: 70% of days historically (n=248), avg high 96°F. Most trips here in March will find more sun than cloud.

Every month in Costa Rica — Guanacaste

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

Historical clear-sky % for Costa Rica — Guanacaste, all months, ERA5 2018–2025.
Month	% Clear	Sample (n)
January	79%	n=248	All destinations →
February	84%	n=226	All destinations →
March ← this page	70%	n=248	All destinations →
April	33%	n=240	All destinations →
May	9%	n=248	All destinations →
June	5%	n=240	All destinations →
July	16%	n=248	All destinations →
August	6%	n=248	All destinations →
September	2%	n=240	All destinations →
October	2%	n=248	All destinations →
November	18%	n=240	All destinations →
December	62%	n=248	All destinations →

Frequently asked

Does it rain in Costa Rica — Guanacaste in March?

Rarely. Only 10% of days in Costa Rica — Guanacaste see measurable rain in March, based on 8 years of ERA5 historical data (n=248 days, 2018–2025). This is a historical average, not a forecast.

Is Costa Rica — Guanacaste good for sun in March?

Yes. Costa Rica — Guanacaste is historically strong for sun in March: 70% of days are clear on average (avg high 96°F, n=248 days, ERA5 2018–2025).

How Costa Rica — Guanacaste compares in March

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

→ Costa Rica — Guanacaste vs Mexico City in March — Mexico City is 71% clear historically
→ Costa Rica — Guanacaste vs Mérida in March — Mérida is 74% clear historically
→ Costa Rica — Guanacaste vs Huatulco in March — Huatulco is 75% clear historically

→ Costa Rica — Guanacaste live forecast — this week’s actual 7-day weather, not historical
→ Best destinations in March — all destinations ranked by March 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.