Let's start with when it's raining season: November, April and May. During those month Safaris are possible, and it is by far not raining every day. Even if, then only for a few hours. But it can get hard if you want to visit remote places.
The mass migration moves from Kenya into the Serengeti in Tanzania in December, January, February, and March. That can be a spectacular time to travel in Tanzania. Climate changes are triggering some changes in the timing of the migration, so check with us if you are interested in traveling on the edges of the normal migratory months.
This doesn't mean that there isn't great game viewing at other times. Off-peak season can be a very relaxing time. The lodges are less crowded and the game reserves not involved in the migratory pathways have as much game as normal. It's all a matter of what you want. Check with us if you have specific time frames in mind for your travel and we can help you plan where to be so you get the best possible game viewing experiences.