East Africa is situated on the equator, so there are not large differences between winter and summer temperatures and the days have more or less the same amount of sunlight. The coast can be relatively humid and inland it could get cold due to the high altitude.
There are two traditional rain seasons, the long rains fall during the months of April and May and short rains fall between October and November.
The Serengeti plains are +-2000m above sea level with an temperature ranging from10 to 20 degrees Celsius. During mid winter the evenings and mornings are often chilly, the Ngorongoro Crater at +- 2200 m above sea level could drop to below freezing during June / July.
The closer to the coast you get the hotter and the more humid with Zanzibar experiencing almost unbearable humidity during the summer months, so please bear this in mind when planning your beach holiday and choose a lodge offering fans and air conditioning.