South Africa is split into two main climatic zones.
The north of the country, including Johannesburg, the Kruger National Park, Limpopo Province, the Kalahari Desert, Durban and northern KwaZulu Natal, is influenced by a sub-tropical climate and receives most rainfall during the warmer summer months from November to March. Temperatures can soar to 40C at this time, especially in the ‘lowveld’ areas of Mpumalanga and KwaZulu/Natal, and it can also be very humid near the coast.
It is usually ‘dry’ from April through to October, and the main winter period runs from May to August. During this time, altitude plays an important factor with temperatures. Along the coast, days are usually warm, but nights can be quite cool. In the ‘highveld’ areas (the Kalahari, Madikwe, Waterberg, Johannesburg and western Limpopo and Mpumalanga provinces), whilst daytime temperatures can reach the high ‘teens’, night temperatures can drop well below freezing and snow can fall on the mountains. September and October see a rapid increase in temperatures as summer approaches.
The south of the country, including Cape Town, the Cape Winelands, Cederberg Mountains, Hermanus, the Karoo Desert, Garden Route, Port Elizabeth and the Eastern Cape, has a more temperate climate and receives most rainfall during the winter months, from April to October. Weather can be extremely varied during this time, swinging from beautifully crisp sunny days to miserable wet and windy conditions. Temperatures are not usually too cold, but snow does often fall on the mountains. During the summer months, from November to March, there is little rain and day time temperatures can reach 40C, particularly away from the coast in the Karoo.
The best time to visit Cape Town and the south of the country is therefore November to March, when you can expect warm, dry weather. In the north of the country, it rather depends on your interests and priorities, but the best safari season is technically during the dry season from May to October, when game viewing conditions are really good. However, the quality of game viewing in the private reserves of northern South Africa is much less affected by season and weather conditions than in much of the rest of Africa, and therefore it is possible to enjoy a very successful safari all year round.