Cameroon's climate varies dramatically from north to south, so the best time to visit depends on where you are going.
The dry season in the south runs from November to February, with a shorter dry spell in July and August. This is the most comfortable time for Douala, Kribi, Limbe, and Yaound. The rains peak in August and September along the coast, when Douala and Limbe can be drenched for days on end. Mount Cameroon and the coast around Limbe is one of the wettest places in Africa -- expect rain even in the dry season.
The western highlands around Bamenda and Foumban are pleasant year-round, with cooler temperatures than the lowlands. Nights can be genuinely chilly above 1,500 meters. The dry season here runs from mid-November through February, which is the best time for the Ring Road.
The north has a more straightforward pattern: a long dry season from October to May and rains from June to September. For wildlife viewing in Waza National Park, visit between January and April, when animals concentrate around the remaining water sources and the vegetation is thin enough to see them. The heat in the north during March and April is extreme -- easily above 40 degrees.
The Mount Cameroon Race of Hope takes place in February. The Ngondo water festival in Douala happens in early December and is one of the most spectacular cultural events in Central Africa. The Nguon festival in Foumban, celebrating the Bamoun kingdom, takes place every two years in December.