Wet season

A wet season storm at night in Darwin, Australia.

In areas where the heavy rainfall is associated with a wind shift, the wet season is known as the monsoon season. Many tropical and subtropical climates experience monsoon rainfall patterns.[10] Rainfall in the wet season is mainly due to daytime heating, which leads to diurnal thunderstorm activity within a pre-existing moist airmass , so the rain mainly falls in late afternoon and early evening in savannah and monsoon regions.

Much of the total rainfall each day occurs in the first minutes of the downpour,[7] before the storms mature into their stratiform stage.[11] Most places have only one wet season, but areas of the tropics can have two wet seasons, because the monsoon trough, or Intertropical Convergence Zone, can pass over locations in the tropics twice per year. However, since rain forests have rainfall spread evenly through the year, they do not have a wet season.[6]

Areas with a savanna climate in Sub-Saharan Africa, such as Ghana, Burkina Faso,[12][13] Darfur,[14] Eritrea,[15] Ethiopia,[16] and Botswana have a distinct rainy season.[17] Also subtropical areas like Florida, South and Southeast Texas, and southern Louisiana have a rainy season.[18] Monsoon regions include the Indian subcontinent, Southeast Asia (including Indonesia and Philippines),[19] northern sections of Australia,[20] Polynesia,[21] Central America,[22] western and southern Mexico,[23] the Desert Southwest of the United States,[24] southern Guyana,[25] and northeast Brazil.[26]

Northern Guyana has two wet seasons: one in early spring and the other in early winter.[25] In western Africa, there are two rainy seasons across southern sections, but only one across the north.[27] Within the Mediterranean climate regime, the west coast of the United States, the southwest coast of Australia and South Africa, the Mediterranean coastline of Italy, Spain, Greece,[28] Lebanon, Syria, Algeria, Morocco, Tunisia, and Turkey, as well as areas further inland in Western Asia which include Jordan, Northern Iraq and most parts of Iran, experience a wet season in the winter months.[29] Similarly, the wet season in the Negev desert of Israel extends from October through May.[30] At the boundary between the Mediterranean and monsoon climates lies the Sonoran desert, which receives the two rainy seasons associated with each climate regime.[31]

The wet season is known by many different local names throughout the world. For example, in Mexico it is known as "storm season". Different names are given to the various short "seasons" of the year by the Aboriginal tribes of Northern Australia: the wet season typically experienced there from December to March is called Gudjewg. The precise meaning of the word is disputed, although it is widely accepted to relate to the severe thunderstorms, flooding, and abundant vegetation growth commonly experienced at this time.[32]

A monsoon in the Vindhya mountain range, central India.

In tropical areas, when the monsoon arrives, high daytime high temperatures drop and overnight low temperatures increase, thus reducing diurnal temperature variation.[33] During the wet season, a combination of heavy rainfall and, in some places such as Hong Kong, an onshore wind, improve air quality.[34]

In Brazil, the wet season is correlated with weaker trade winds off the ocean.[26] The pH level of water becomes more balanced due to the charging of local aquifers during the wet season.[35] Water also softens, as the concentration of dissolved materials reduces during the rainy season.[36] Erosion is also increased during rainy periods.[7]

Arroyos that are dry at other times of the year fill with runoff, in some cases with water as deep as 10 feet (3.0 m).[37] Leaching of soils during periods of heavy rainfall depletes nutrients.[37] The higher runoff from land masses affects nearby ocean areas, which are more stratified, or less mixed, due to stronger surface currents forced by the heavy rainfall runoff.[38]

• Akhet
• East Asian rainy season
• Dry season