Observations from five inverted echo sounders deployed between 10¿W and 38¿30'W along the equator during the spring and summer of 1983 are presented. The annual development of the eastward acting zonal pressure gradient is described and related to the observed zonal wind stress. The minimum and maximum basin wide gradients are observed in mid-April and in the latter part of July, respectively. The upwelling season in the Gulf of Guinea is identified at the easternmost sounder during May, June, and July. Pulses in thermocline displacement (first deepening, then shallowing) propagate eastward across the basin at speeds of 2.8 and 2.1 m s-1. They arrive at 10¿W at the onset and just after the cessation of the seasonal upwelling at the location. Their initialization is related to relaxation periods in the zonal wind. For four of the last five years, the time of the pulse preceding the upwelling is tentatively identified.