When you're planning a trip to Africa, knowing when the rainy season or wet season and the dry season falls, helps determine the best time to go. In general, the best time to go on safari is during the dry season because water is scarce and animals will congregate around existing water holes. The grass is lower affording better visibility and the dirt roads are navigable. All of these factors help you enjoy a successful safari. But the heat can be intense depending on where and when you plan to travel. So while cold temperatures are not a huge issue in Africa (although it does snow in some parts), hot weather can make or break your trip.
In some regions the heat during the rainy season is worse than during the dry season because of the added discomfort of humidity. This is especially the case as you get closer to the coast. The weather is unpredictable of course, and rains do fail causing untold hardship to millions of subsistence farmers in Africa. Some years too much rain falls on the parched soil, and floods cause huge damage. In general, the "wet season" means buckets of rain fall from sky for a few hours a day, and then it will go back to being nice and sunny. If you're looking to save some money, traveling during the wet season is the way to go. It's also the best time to see birds and baby animals.
The Rainy and Dry Season in East Africa - The hottest time of year in East Africa is during the dry season from December to March. Northern Tanzania and Kenya experience two rainy seasons, the long rains from April to June and a shorter rain from November to December.
The Rainy and Dry Season in Southern Africa - The dry season in southern Africa is during the cooler months from May - August. The rainy (wet) season is also the hottest time of year in southern Africa, and generally runs from November to March.
Winter and Summer in North Africa - North Africa generally has mild winters (December - February), perfect for visiting tombs and monuments in hot deserts or taking a camel safari in the Sahara. The summer months in North Africa (June - September) are blazing hot. Head to the beaches or mountains if you plan to visit during this time, or make sure your hotel has a pool to cool off in the heat of the day. Summers are usually bone dry.
Winter and Summer in South Africa - South Africa is far south enough from the equator to enjoy a somewhat traditional summer and winter season (although its geography doesn't make this quite so simple). South Africa's summers (November to March) are generally warm with average temperatures around 77 Fahrenheit (25 C).
If you are traveling to the Indian Ocean islands of Mauritius, Madagascar or Reunion, avoid the rainy season January - March because it is also "cyclone" season. Cyclones and hurricanes are extremely rare in The Seychelles.