A riptide is an extremely strong current that occurs when the ocean tide pulls water through a small area such as a bay, lagoon or other confined body of water. Riptides occur during the ebb tide and are reversing currents. A riptide is very hazardous to swimmers. The word riptide is sometimes rendered as two words, rip tide.
A rip current is a dangerous current that occurs on a beach. Water is pushed up on the beach through the action of breaking waves, this water must escape back to sea. If the backwash water can dissipate along the shore uniformly, there is no problem. But if there is a feature on the beach that allows the water to return to the ocean more quickly, such as a gap in a sandbar, then that faster-moving water becomes a rip current. Rip currents are generally not very wide, but may pull a swimmer out past the waves into deep water.
An undertow occurs when large waves break at a beach, the uprush and backwash of water occur in quick succession. When one of these large waves breaks over a swimmer’s head, he feels as if he is being dragged under the water. An undertow does not pull a swimmer into deeper water. The word undertow may also be used to mean an influence or emotion that lies underneath the surface of a particular incident or happening.
Examples
Hugh Jackman and his children were swimming at Sydney’s Bondi Beach on Saturday when a riptide came through. (The Hollywood Reporter)
The whales follow the rip tide that escapes the bay before low tide, feeding on plankton that are sucked out to sea. (The Valley Advocate)
Gusty east winds will create a high risk of rip currents along the beaches of Palm Beach County through Thursday morning, the National Weather Service said. (The Palm Beach Post)
When the mother returned to the beach, her children had been swept up by the undertow and drowned. (The Dothan Eagle)
In his later decades, criss-crossing Europe and North Africa, Strand continued to produce work that had a subtle but unmistakable political undertow. (The New Yorker Magazine)