Puerto Rico weather by month

In San Juan, 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 18 and lasts for 5.3 months, ending around April 28. The clearest month is February, when the sky is clear, mostly clear, or partly cloudy 88% of the time on average.

The cloudier part of the year begins around April 29 and lasts for 6.7 months, ending around November 17. The cloudiest month is September, when it is overcast or mostly cloudy 55% 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 Juan is typically light breeze, near 14 km/h, and varies moderately with the seasons.

The windier part of the year lasts 2.8 months, from around Jun 1 to Aug 25. The windiest month is July, averaging about 17 km/h (light breeze).

The calmer part of the year runs from around Aug 26 to Dec 11, with October the calmest month at about 11 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 Juan receives about 5.7 kWh/m² a day of solar energy on average — bright — with a clear seasonal swing between 4.3 and 6.6 kWh/m².

The brighter stretch of the year lasts 6.7 months, from around Mar 2 to Sep 21. The brightest month is June, averaging about 6.5 kWh/m² (intense).

The dimmest month is December, down near 4.4 kWh/m² — roughly 33% less than the June peak.