Storms usually induce a surge that causes the water level to reach a higher position compared to normal conditions. In addition, wave energy is usually higher than normal under storm conditions so that currents and subsequent sediment transport can induce dramatic morphological changes, including severe erosion. This chapter aims to present the main processes that control water level variations and hydrodynamic circulation under storm conditions. The section following this introduction presents the main mechanisms that control storm surges: atmospheric pressure gradients, surface stress and short-wave dissipation. The third section presents the mechanisms that drive the hydronamic circulation along the coast: longshore currents, bed return flows, infragravity waves and swash dynamics. This chapter concludes with some perspectives and challenges.