Air-sea interaction under strong gap-flow winds to 30 meters per second occurs in the Gulf of Tehuantepec. An internal boundary layer develops and spreads off-shore under strong subsidence. Measurements of meteorological parameters, turbulence, and surface waves were made with the NCAR C-130 aircraft. Surface flux measurements were made from tracks at 30 meter altitude from which bulk coefficients (drag, Stanton and Dalton numbers) were obtained. Stress divergence in the inhomogeneous boundary layer was approximately balanced by the pressure gradient term. There is evidence of a hydraulic jump occurring. Supported by the Division of Ocean Sciences, National Science Foundation.