Temperature and rainfall patterns vary in response to the movement of a high-pressure belt that circles the globe between 25º and 30º south latitude during the winter and low-pressure systems that occur during summer. There is very little difference in average temperatures from south to north, however, in part because the inland plateau rises slightly in the northeast. For example, the average annual temperature in Cape Town is 17ºC, and in Pretoria, 17.5ºC, although these cities are separated by almost ten degrees of latitude. Maximum temperatures often exceed 32ºC in the summer and reach 38ºC in some areas of the far north. The country’s highest recorded temperatures, close to 48ºC, have occurred in both the Northern Cape and Mpumalanga.

Frost occurs in high altitudes during the winter months. The coldest temperatures have been recorded about 250 kilometres northeast of Cape Town, where the average annual minimum temperature is -6.1º C. Record snowfalls (almost fifty centimetres) occurred in July 1994 in mountainous areas bordering Lesotho.

Climatic conditions vary noticeably between east and west, largely in response to the warm Agulhas ocean current, which sweeps southward along the Indian Ocean coastline in the east for several months of the year, and the cold Benguela current, which sweeps northward along the Atlantic Ocean coastline in the west. Air temperatures in Durban, on the Indian Ocean, average nearly 6º C warmer than temperatures at the same latitude on the Atlantic Ocean coast. The effects of these two currents can be seen even at the narrow peninsula of the Cape of Good Hope, where water temperatures average 4º C higher on the east side than on the west.

Rainfall varies considerably from west to east. In the northwest, annual rainfall often remains below 200 millimetres. Much of the eastern Highveld, in contrast, receives 500 millimetres to 900 millimetres of rainfall per year; occasionally, rainfall there exceeds 2,000 millimetres. A large area of the centre of the country receives about 400 millimetres of rain, on average, and there are wide variations closer to the coast. The 400-millimetre “rainfall line” has been significant because land east of the rainfall line is generally suitable for growing crops, and land west of the rainfall line, only for livestock grazing or crop cultivation on irrigated land.