Barotropic semidiurnal tidal currents measured off the coast of northern California during the Coastal Ocean Dynamics Experiment (CODE) are examined. While the pressure field is consistent with the idea that the semidiurnal surface tide is dominated by a Kelvin wave, a high degree of variability over alongshore distances of the order of 25 km is observed in the velocity field. Comparison with existing models used to predict tidal velocities from sea level measurements cannot account for this spatial structure. Perturbation analysis of a Kelvin wave propagating along a coastal boundary with bumps characterized by an alongshore length scale much less than the Rossby radius of deformation shows effects on the velocity and pressure field which decay offshore with the alongshore scale of the bumps. The effect on the velocity field exceeds that on the pressure field by a factor equal to the ratio of the Rossby radius to the alongshore scale of the bumps. We conclude that the alongshore structure observed in the measured barotropic semidiurnal tidal currents may be due in part to the local variations in the coastline geometry in the CODE region. ¿American Geophysical Union 1987