Subtropical areas are those adjacent to the tropics, usually roughly defined as the ranges 23.5-40° N and 23.5-40° S latitude. These areas typically have very warm to hot summers, but non-tropical winters. In certain areas of the world, the subtropics are plagued by tropical cyclones that originate in the tropics in the summer and fall.
Subtropical climate implies that the air temperature usually does not go below freezing (0°C). This is a threshold temperature for a gamut of plants, and applies to coastal California, southern Florida, coastal Australia, and coastal South Africa, for example. The pole ward limit of such climates is higher on the west coasts of the northern continents and lower on the east coasts, because occasional Winter cold snaps reach farther south in the east.
South Africa is located at the extreme south of Africa, with a long coastline that stretches more than 2,500 kilometers or 1,550 miles and across two oceans, the Atlantic and the Indian. South Africa has a great variety of climate zones, from the extreme desert of the Kalahari near Namibia to lush subtropical climate along the border with Mozambique. It quickly rises over a mountainous escarpment towards the interior plateau known as the Highveld. Even though South Africa is classified as semi-arid, there is considerable variation in climate as well as topography.
Humid subtropical climate usually occurs in the interiors of continents, or on their east coasts, between the latitudes of 25° and 37°. Unlike the Mediterranean climates, the summers are humid due to unstable tropical air masses, or onshore Trade Winds. In eastern Asia, winters can be dry (and colder than other places at a corresponding latitude) because of the Siberian high pressure system, and summers very wet due to monsoonal influence.
A monsoon is a periodic wind, especially in the Indian Ocean and southern Asia. The word is also used to label the season in which this wind blows from the southwest in India and adjacent areas that is characterized by very heavy rainfall, and specifically the rainfall that is associated with this wind. Monsoons are caused by the fact that land heats up and cools down more quickly than water. Thus, in summer, land reaches a higher temperature than the ocean. The hot air over the land tends to rise, creating an area of low pressure. This creates an extremely constant wind blowing toward the land. Associated rainfall is caused by the moist ocean air being diverted upward by mountains, which causes cooling, and in turn, condensation. As monsoons have come to be better understood, the definition has been broadened to include almost all of the phenomena associated with the annual weather cycle within the tropical and subtropical continents of Asia, Australia, and Africa and the adjacent seas and oceans. It is within these regions that the most vigorous and dramatic cycles of weather events on Earth take place. Monsoons are similar to sea breezes, but they are much larger in scale, stronger, and are more constant and fast.