The rainfall field over West Africa is characterized by a zone of maximum precipitation that migrates north and south throughout the course of the June to October rainy season. The zone of maximum rainfall lies to the south of the surface position of the ITCZ and is more closely linked to shifts in the location and structure of the mid-troposheric African Easterly Jet (AEJ). In particular, there are two sharp excursions of the rainfall maximum early and late in the season that are linked to pronounced shifts in the location of the jet. Maximum rainfall occurs in August and September, when the jet is strongest and furthest north. Interannual fluctations in the seasonal cycle of rainfall are clearly linked to changes in the structure and location of the jet. In equatorial Africa, a similar jet exists just south of the equator. It appears to bear some relationship to the migration of the zone of maximum rainfall in this region. It first appears in July or August and is best developed in September to October, the main rainy season in the area of a double maximum in the seasonal cycle. The jet is not strongly apparent in the weaker rainy season of March-to-May