South Africa has three major climatic zones, and Austral seasons so their summer corresponds to our winter, and vice versa.
The Cape Region and Garden Route have a climate very much like that of the south of France: summer runs from October to April and is warm with some rain (and more wind in Cape Town). Late summer is a very pleasant time: cooler, but quite dry and less windy. Winters, from May through to September are cool and traditionally wetter, although this is getting harder to predict.
In KwaZulu-Natal a sub-tropical climate ensures hot, humid summers along the coast with more rain than in the winter, which is pleasantly warm during the day and cooler at night.
The Wild Coast has a milder version of the same climate, a few degrees cooler and not as humid.
The Lowveld, around the Kruger Park, and the Highveld plateau that dominates much of the rest of the country experience hot summers with short, spectacular storms, and pleasant winters with gentle daytime temperatures and little rain. The Highveld is cooler than the Lowveld, and winter nights can fall to freezing and below.