The African easterly jet is a region of the lower troposphere over West Africa where the seasonal mean wind speed is maximum and easterly. The jet develops because heating of the West African land mass during the Northern Hemisphere summer creates a surface temperature and moisture gradient from the Gulf of Guinea and the Sahara, and the atmosphere responds by generating vertical wind shear to maintain thermal wind balance. During the mature phase of the West African Monsoon (August to September) maximum mean wind speeds in the jet of approximately 13 m/s are located around 4°N—5°N at a height of 4 km (or 650 mb).
The jet exhibits both barotropic and baroclinic instability, which produces synoptic scale, westward propagating disturbances in the jet known as African easterly waves. A small number of meso-scale storm systems embedded in these waves develop into tropical storms and hurricanes after they move from West Africa to the tropical Atlantic.
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