Description

A tropical wave (also called easterly wave, tropical easterly wave, and African easterly wave), in and around the Atlantic Ocean, is a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which moves from east to west across the tropics, causing areas of cloudiness and thunderstorms. Tropical waves form in the easterly flow along the equatorial side of the subtropical ridge or belt of high pressure which lies north and south of the Intertropical Convergence Zone (ITCZ).

Tropical waves are generally carried westward by the prevailing easterly winds along the tropics and subtropics near the equator. They can lead to the formation of tropical revolving storms in the north Atlantic and notheastern Pacific basins.

Tropical wave formation in the Atlantic

Tropical waves in the Atlantic basin develop from low-pressure disturbances, which develop as far east as Sudan in east Africa, and drift across the continent into the Atlantic Ocean. These are generated or enhanced by the African Easterly Jet. The clockwise circulation of the transoceanic high-pressure cell or anticyclone centered near the Azores (known as the Azores High) impels  waves away from the coastal areas of Africa towards North America.

Tropical waves formation in North Atlantic [Source: Wikipedia, Author: NOAA]. The role of the Azores High in impelling tropical waves westward is a major contributor to hurricane formation.

Tropical cyclones in the northeastern Pacific may be formed out of tropical waves that also originate in North Africa having moved across the Atlantic, developed into tropical cyclones and crossed into the Pacific.

Tropical wave formation in the western Pacific basin

Low level disturbance fuelled by warm ocean water and rising air leads to troughs of low pressure that move westwards propelled by the Pacific trade winds. These tropical waves can develop into tropical storms (Typhoons). El Nino years can lead to increased activity due to warmer sea temperatures.