Western Kenya does not have a dry season as such — it sits on the wet side of the East African climate — but there are clear differences between months. The driest periods are January and February and again in June to early August, when daytime temperatures are pleasantly cool (the equator at altitude) and the forest paths are usable without becoming a mud bath. April and November are the long-rains and short-rains peaks; visits are possible but plan for slippery trails and frequent afternoon downpours.
For birdwatchers, the best window is the boreal winter from October to April, when Palaearctic migrants are present in addition to the resident forest species. For walkers and general visitors, June and July are the most consistent. The Saturday morning bullfights in the villages around Kakamega happen year-round but tend to be most frequent during the months between the two rainy seasons, when farmers have the time and the bulls have the energy.