Vidal-Juárez, T.; Ruiz de Alegría-Arzaburu, A.; Mejía-Trejo, A.; García-Nava, H., and Enriquez, C., 2014. Predicting barrier beach breaching due to extreme water levels at San Quintín, Baja California, México.This study comprises a first approach to numerically determine the hydrodynamic conditions leading to barrier breaching at San Quintín, located in the northwestern coast of the Baja California peninsula in Mexico. The barrier is backed by a large coastal lagoon, fronted by a field of submerged volcanoes located several kilometers off the coast and is exposed to large incoming wave energy dominated by the Pacific swell. The narrowest barrier beach sections are vulnerable to flooding due to overwash events that take place during concurrent high spring tides, energetic storm waves and a range of storm surge levels. Here, the conditions to barrier overwash and breaching occurrence are identified, and the extent of the floods is numerically quantified. For that purpose, the Delft3D hydrodynamic model is applied coupling waves and flows to simulate a series of scenarios, which comprise storm waves of different magnitudes and periods approaching from typical directions, and coupled to spring tides and several storm surge levels. As a consequence of the presence of submerged volcanoes off the coast, the incoming wave energy is mostly concentrated at two specific locations along the barrier beach, which correspond to the lowest and narrowest barrier locations. Due the large distance between both sites, longshore variations are not expected to be as strong as the cross-shore. Numerical results suggest that the barrier is susceptible to flooding during spring tides combined with extreme waves of significant wave heights larger than 3.5 m and a peak period of 7.5 s, and storm surge levels exceeding 0.9 m, which may lead to breaching.