French Guiana weather by month

In Cayenne, 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 July 5 and lasts for 4.6 months, ending around November 22. The clearest month is September, when the sky is clear, mostly clear, or partly cloudy 82% of the time on average.

The cloudier part of the year begins around November 23 and lasts for 7.4 months, ending around July 4. The cloudiest month is May, when it is overcast or mostly cloudy 76% 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 Cayenne is typically light breeze, near 16 km/h, and varies moderately with the seasons.

The windier part of the year lasts 5.3 months, from around Dec 7 to May 15. The windiest month is February, averaging about 19 km/h (light breeze).

The calmer part of the year runs from around May 16 to Dec 6, with July the calmest month at about 12 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.

Cayenne receives about 5.1 kWh/m² a day of solar energy on average — bright — with a clear seasonal swing between 4.4 and 6.3 kWh/m².

The brighter stretch of the year lasts 4.3 months, from around Jul 16 to Nov 22. The brightest month is September, averaging about 6.2 kWh/m² (intense).

The dimmest month is May, down near 4.5 kWh/m² — roughly 28% less than the September peak.