Benin has two rainy and two dry seasons. The principal rainy season is from April to late July, with a shorter less intense rainy period from late September to November. The main dry season is from December to April, with a short cooler dry season from late July to early September.
Temperatures and humidity are high along the tropical coast. In Cotonou, the average maximum temperature is 31 °C (87.8 °F); the minimum is 24 °C (75.2 °F). Variations in temperature increase when moving north through a savanna and plateau toward the Sahel. A dry wind from the Sahara called the harmattan blows from December to March.
Grass dries up, the vegetation turns reddish brown, and a veil of fine dust hangs over the country, causing the skies to be overcast. It is also the season when farmers burn brush in the fields.