Obliquely incident waves breaking on a beach drive an alongshore mean current that can exceed 1m/sec. This current, localized to the surf zone and highly sheared in thecross-shore direction, is unstable. The growing instabilities, known as shear waves, are vorticity waves with periods of a few minutes and alongshore wavelengths of a few 100m. Shear waves observed at five cross-shore locations within a few 100m of the shoreline of a sandy beach are compared with numerical solutions of the nonlinear shallow water equations. As in previous model-data comparisons within the surfzone where V is strong and shear waves are energetic (Ozk ¨ an-Haller and Kirby, JGR 1999), modeled and observed shear wave alongshore phase speeds are similar, and observed and simulated shear wave root-mean-square velocity fluctuations are both 10-20% of V . Farther offshore, where V and shear wave energy levels are reduced, the observed alongshore phase speeds usually decrease to roughly V . A cross-shore decrease in the numerically simulated phase speed is associated with the alongshore advection, by the relatively weak and unsheared V , of features shed from the strong, sheared flow further onshore. Although finite amplitude effects limit shear wave growth, aspects of the fully nonlinear numerical solutions (and the observations) resemble the linearly unstable modes.