The Cape Peninsula has a Mediterranean-type climate with well-defined seasons. In the winter months, May through August, cold fronts sweep across the Atlantic and bombard the Peninsula with rain and the north-west gales - an apt reminder of why the early explorers referred to it as the Cape of Storms. The winters are cool with an average minimum temperature of about 7° C. Most of the rainfall occurs in winter, but due to the topography the rainfall varies quite dramatically.
In the valleys and coastal plains it averages 500mm per year, while in the mountainous areas it can average as much as 1500mm a year.Winter is nonetheless a particularly beautiful time at the Cape as the vegetation regains its verdure and water pours from the mountain chain’s waterfalls, rivulets and ravines. Summer, on the other hand, is warm and dry. During these months - November through February - the Peninsula is exposed to the strong (sometimes gale force) , relentless South-East wind known locally as the Cape Doctor because it blows away pollution and cleans the air. The south-easter is caused by the South Atlantic high pressure cell which sits off the southern tip of Africa over this period, resulting in the many clear, sun-filled days which visitors find so appealing. Summer temperatures are relatively comfortable with the average maximum around 26° C.
The Cape Doctor Wind
The prevailing Spring and early Summer wind , the South-Easter (otherwise known as the "Cape Doctor") arises as a spin-off from anticyclones deep in the Southern ocean. It arrives at the peninsula by way of False Bay, its velocity often being given a boost by the "corner effect" round Cape Hangklip.
One arm of the South-Easter sweeps around the eastern flanks of Table Mountain, where its moisture, picked up from the ocean and the warm waters of False Bay, helps to keep the vegetation green through the heat of summer.
It is also a vital factor in the pollination of many plants, including the Silvertrees. The South-Easter continues on around Devil's Peak, before descending on the city.
There, it behaves somewhat in the manner of a trapped tiger, careering around in the bowl between mountain and sea. A couple of days of this is enough to purge the city's air - nowadays it is the smog instead of the plague of old which is banished. The South-Easter tends to overdo the cure, outstaying its welcome. A possible record was its performance in November 1936, when it howled without a break for 15 days, ravaging suburban gardens and penning the staff in the upper cable station for 5 days.