The Casamance has two seasons: dry (November to May) and wet (June to October). The dry season is the obvious time to visit — roads are passable, the river is calm, and the humidity is bearable. December to February is the most comfortable period, with temperatures in the low 30s and cool evenings.
The wet season transforms the landscape. Rice paddies flood, mangrove channels fill, and the forest turns an intense green. Travelling in the wet season is difficult — roads can become impassable and some village campements close — but pirogue travel on the river is actually easier, and the countryside is beautiful. If you can manage the logistics, a visit in September or October is not as inadvisable as people often suggest.
The mango season, from April to June, is a good time to be in Ziguinchor — the market is full of fruit and the mood is festive. Avoid the peak of the dry season harmattan (December–January) if dust and dry air bother you. The Diola sacred forest initiation ceremonies (called bukut) happen on an irregular cycle, roughly every generation, and are not open to outsiders — but the associated festivities in Oussouye and nearby villages are one of the most extraordinary things you can witness in West Africa.