Costa Rica weather by month

In San Jose, the average share of the sky covered by clouds shows significant seasonal variation over the course of the year.

The clearer part of the year begins around November 28 and lasts for 4.7 months, ending around April 18. The clearest month is February, when the sky is clear, mostly clear, or partly cloudy 58% of the time on average.

The cloudier part of the year begins around April 19 and lasts for 7.3 months, ending around November 27. The cloudiest month is September, when it is overcast or mostly cloudy 98% of the time.

This is the average sustained wind speed at the standard 10 metres above open ground — the steady flow a weather station reports, not the sharper gusts that come and go, which can run half again as fast. It's the number that says whether a place is generally breezy or calm.

Across the year, average wind speed in San Jose is typically calm, near 6 km/h, and varies little with the seasons.

The windier part of the year lasts 5.0 months, from around Nov 18 to Apr 18. The windiest month is January, averaging about 8 km/h (calm).

The calmer part of the year runs from around Apr 19 to Nov 17, with September the calmest month at about 4 km/h.

Solar energy is how much sunlight actually reaches the ground each day, measured in kilowatt-hours per square metre (kWh/m²) — the combined effect of how long the sun is up, how high it climbs, and how much cloud gets in the way. It's the raw fuel a solar panel has to work with: for scale, 1 kWh/m² a day is dim and wintry, while 7+ is desert-bright.

San Jose receives about 4.5 kWh/m² a day of solar energy on average — bright — with a clear seasonal swing between 3.6 and 5.9 kWh/m².

The brighter stretch of the year lasts 4.1 months, from around Jan 6 to May 9. The brightest month is March, averaging about 5.8 kWh/m² (bright).

The dimmest month is November, down near 3.6 kWh/m² — roughly 37% less than the March peak.