Subtropical climates are often characterized by hot summers and mild winters with infrequent frost. Most subtropical climates fall into two basic types: humid subtropical, where rainfall is often concentrated in the warmer months (for example Brisbane, Queensland or Jacksonville, Florida), and Mediterranean or dry-summer, where rainfall is concentrated in the cooler months (for example Naples, Italy or Los Angeles, California).
A great portion of the world's deserts are located within the subtropics, due to the development of the subtropical ridge. Areas bordering warm oceans (typically on the southeast sides of continents) are prone to locally heavy rainfall from tropical cyclones, which can contribute a significant percentage of the annual rainfall. Areas bordering cool oceans (typically on the southwest sides of continents) are prone to fog, aridity, and dry summers. Plants such as palms, citrus, mango, pistachio, lychee, and avocado are grown in the subtropics.
Heating of the earth near the equator leads to large amounts of upward motion and convection along the monsoon trough or intertropical convergence zone. The upper-level divergence over the near-equatorial trough leads to air rising and moving away from the equator aloft. As the air moves towards the mid-latitudes, it cools and sinks, which leads to subsidence near the 30th parallel of both hemispheres. This circulation is known as the Hadley cell and leads to the formation of the subtropical ridge. Many of the world's deserts are caused by these climatological high-pressure areas, located within the subtropics. This regime is known as an arid subtropical climate, which is generally located in areas adjacent to powerful cold ocean currents. Examples of this climate are the coastal areas of southern Africa (Namibia, South Africa), the south of the Canary Islands and the coasts of Peru and Chile.
These climates do not routinely see hard freezes or snow, which allows plants such as palms and citrus to flourish. As one moves toward the tropical side the slight winter cool season disappears, while at the poleward threshold of the subtropics the winters become cooler. Some crops which have been traditionally farmed in tropical climates, such as mango, litchi, and avocado, are cultivated in the subtropics. Pest control of the crops is less difficult than within the tropics, due to the cooler winters.
The humid subtropical climate is a subtropical climate type characterized by hot, humid summers with frequent tropical downpours of short duration and warm, and frequently dry winters. In summer, the subtropical high pressure cells provide a sultry flow of tropical air with high dew points, and daily thundershowers are typical, though brief. Normally, rainfall is concentrated in the warmest months of the year. At times, the average annual precipitation may be more evenly distributed throughout the year, or a spring maximum is present. With decreasing latitude most humid subtropical climates typically have drier winters and wetter summers.