Narrow, jetlike stream of water that flows sporadically seaward for several minutes, in a direction perpendicular to a beach. The term riptide is a misnomer because the currents are in no way related to tides. Rip currents form at long coasts that are approached by wave trains that are nearly parallel to the shoreline. In shallow water, normal wave motion displaces the water small distances shoreward with each passing wave. During periods of large waves, water builds up at the beach and cannot escape as longshore currents, which require oblique wave approach. The buildup continues until water can escape by surging for several minutes through a low point in a breaker, creating an undertow that can be dangerous for swimmers.