The African easterly jet is a region of the lower troposphere over West Africa where the seasonal mean wind speed is at a maximum and the wind is easterly. The temperature contrast between the Sahara Desert and the Gulf of Guinea causes the jet to form to the north of the monsoon trough. The jet's maximum wind speeds are at a height of 3 kilometres (1.9 mi). The jet moves northward from its south-most location in January, reaching its most northerly latitude in August. Its strongest winds are in September while it begins shifting back towards the equator. Within the easterly jet, tropical waves form. Convective complexes associated with these waves can form tropical cyclones. If the jet is south of its normal location during August and September, tropical cyclogenesis is suppressed. If desertification continues across Sub-Saharan Africa, the strength of the jet could increase, although tropical wave generation probably would decrease, which would decrease the number of tropical cyclones in the Atlantic basin.