For the most part, Benin is very hot and humid, especially in the south. Like most other West African countries, there are two dry and two rainy seasons. From October to April, Benin is dry, whereas it is rainy from May to September.
South of Savalou, especially in the west, the climate is typically equatorial – hot and humid, with a long dry season from December to March, in which the dry harmattan blows in the northeasterly to southwesterly direction. The great rains fall from March to July; there is a short dry season from July to September and a short wet season from September to November. In the southwest, average rainfall is considerably lower and the dry season longer. Northern Benin has a typical tropical climate, with only one wet season (May to September, with most rain in August) and a hot dry season in which the harmattan blows for three or four months. The highest midday temperatures are in January and the lowest in August, but throughout the year the range between midday and night temperatures is great, as much as 15.5C (28F) in the hot season. Although rainfall, which is highest in central Benin (53 inches), decreases as one moves northward, it remains high (40 inches) in most of northern Benin.
The best time to visit the Southern area is from December to March and July/August while visiting period for the Northern part of the country is best between December and April.