French Guiana has a tropical climate with high humidity and rain year-round. The coast is warm and oppressive; the interior is slightly cooler but no drier.
There are two dry seasons and two wet seasons each year:
Long dry season: July to November — the best time to visit. Rain is less frequent, rivers are lower (making jungle trekking easier), and wildlife concentrates around water sources. Saul is most accessible in this period and accommodation fills up, so book ahead.
Short dry season: February to mid-March — a shorter window of drier weather. Useful if July–November doesn't work for you.
Long wet season: December to January — heavy rains, flooded forest trails, river transport can be disrupted. The Hmong market at Cacao on Sundays still draws visitors regardless.
Short wet season: April to June — another rainy period with frequent afternoon downpours.
Sea turtles nest on the Awala-Yalimapo beach from April to July, peaking in May and June. If that's your priority, the "wrong" season for dry conditions is actually the right one.
Temperatures stay between 25°C and 32°C (77–90°F) throughout the year. Humidity makes it feel hotter. Evenings on the coast get some breeze; the interior does not.
Avoid planning a space launch visit to Kourou without checking the Arianespace schedule in advance — launches are infrequent and often delayed.