Looking at equatorial Africa in Google Maps, the western part – Guinea, the Congo – is the dark green of tropical rain forest that I would expect of a wet equatorial region, by analogy with the Amazon basin and similar latitudes in east Asia.
By contrast, the eastern part – Kenya, Tanzania – is the light green of savanna and the light brown of semidesert or desert, indicating much drier conditions that at other longitudes, are more associated with the edges of the Hadley cells, 20-30 degrees away from the equator.
That's not at all the pattern I would've expected. By the basic logic of convection cells, plus analogy with other continents, I would've expected moist conditions across the width of equatorial Africa, but failing that, because the prevailing winds in the tropics blow from the east, I would've expected the eastern part of the continent (which gets wind from the Indian Ocean) to be wet and the western part (which gets wind that has blown some distance over land) to be drier.
Why is it that the western part of equatorial Africa is wet and the eastern part is dry?