In this study we examine the surface layer heat balance using wind, current, and temperature data from equatorial moorings along 165¿E. The analysis focuses primarily on daily to monthly time scale variations during the 1986--1987 El Ni¿o/Southern Oscillation event. The period is one of high mean sea surface temperatures (>29 ¿C) and frequent outbreaks of westerly winds. We infer that evaporative cooling related to wind speed variations accounts for a significant fraction of the observed sea surface temperature (SST) and upper ocean heat content variability. This evaporative heat flux converges nonlinearly in the surface layer, giving rise to larger temperature variations in the upper 10 m than below. Other processes examined (wind-forced vertical advection and entrainment, lateral advection) were negligible or of secondary importance relative to evaporative cooling. A large fraction of the SST and surface layer heat content variance could not be directly related to wind fluctuations; this unexplained variance is probably related to shortwave radiative fluxes at the air-sea interface.