An air-sea interaction surface mooring was deployed in the eastern tropical Pacific Ocean at 10N, 125W during the 1997/1998 ENSO to obtain accurate estimates of air-sea fluxes as part of the Pan American Climate Study (PACS). During the 18-month deployment, a full seasonal cycle was recorded, including the migration of the ITCZ over the mooring. The high-resolution measurements of surface meteorological properties and incoming short and long wave radiation allow accurate computation of the air-sea fluxes of heat, freshwater, and momentum. The measurements are used to characterize the variability in the near-surface atmospheric boundary layer at the site during the 1997/1998 ENSO. It is found that the net heat flux into the ocean is higher while the ITCZ is over the site because reduced wind speeds contribute to a substantial decrease in evaporation. Furthermore, the air-sea fluxes are used in conjunction with subsurface measurements of temperature, salinity, and velocity to examine the local oceanic response during two contrasting regimes of meteorological variability defined as ITCZ and non-ITCZ conditions. Through the use of a one-dimensional oceanic boundary layer model, it is found that the high winds of the non-ITCZ regime generate strong inertial oscillations in the oceanic boundary layer, and the coupling of these oscillations with the large-scale geostrophic currents induce mixing and deepening of the thermocline through Kelvin-Helmholtz instability.