SAVANNAH, Ga. (WSAV) — The late summer and into the fall and winter seasons are typically when we see frequent wave activity along the east coast. This is caused by several factors, one being increased tropical development during the fall due to warm sea surface temperatures, calm vertical wind shear, and less Saharan dust. Additionally, as we head into the late fall and winter months large dips in the jet stream will cause systems to track into the southeast and up the east coast producing swell from Florida to New England.
Whether it be from a tropical system, cold front, or a winter storm, large waves generated by these systems can travel hundreds of miles to shore and increase the rip current risk, cause beach erosion, and even allow surfers to catch a few sweet rides!
TEAHUPO'O, FRENCH POLYNESIA - JULY 27: Caroline Marks of Team United States rides a wave during round one of surfing on day one of the Olympic Games Paris 2024 at on July 27, 2024 in Teahupo'o, French Polynesia. (Photo by Sean M. Haffey/Getty Images)
What is a wave and how do they form?
A wave is a disturbance along the surface of a body of water which is primarily generated through wind interactions with the surface. As the wind blows over the surface of the water, friction transfers energy into the water forming ripples that grow larger as wind speeds increase. As a wave is produced, it travels out and away from the source of wind, however, the water itself is not moving.
When energy moves through a body of water, molecules will oscillate up and down creating a circular pattern which allows for energy to be transferred horizontally over vast distances in the form of a wave. A great way to see this take place is by watching a buoy, as a wave moves in, the buoy will appear to shift forward and upward as the wave moves beneath. As the wave passes the buoy will fall back down and end up in the same position that it started before the wave came through.
Once a wave moves near shore and into shallow bodies of water it will be able to break, typically over sandbars across our region but they can also break over reefs and rocky structures. It is in these shallow bodies of water where the depth of the water column decreases causing the height of the wave to increase. Next, the wave slows down due to friction with the bottom of the sea floor and when the bottom of the water column is moving slower than the crest, the wave will break.
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A few other ways that waves can be created are by the force of gravity and water displacement. Let's start with gravity, these are sometimes referred to as tidal bores. For these waves to form you need a large difference in tides. These waves most commonly form in parts of the world with a tidal range larger than 20 feet.
Additionally, a location is needed where the incoming high tide can enter a shallow, narrow river, harbor, or estuary. As the water pushes into these waterways along with the rapidly rising tide, the shallow floor causes the water column to rise, forming a wave. With the help of friction, the wave crest can exceed the speed of the wave itself, allowing it to break and flow upstream for miles. A body of water that regularly experiences tidal bores is Turnagain Arm, a waterway in the northwestern portion of the Gulf of Alaska. The wave that breaks here can go upstream for up to 50 miles!
Brazilian surfer Naysson Costa prepares to ride the tidal bore wave known as "Pororoca," during the Amazon Surf Festival held in the Canal do Perigoso, or "Dangerous Channel," at the mouth of the Amazon River near Chaves, Marajo Island archipelago, Para state, Brazil, Monday, June 5, 2023. The Pororoca, a word from an Amazonian Indigenous dialect that means "destroyer" or "great blast," happens twice a day when the incoming ocean tide reverses the river flow for a time. (AP Photo/Eraldo Peres)
Next, we have waves that are created through water displacement. These are known as tsunamis and they have the power to destroy coastal communities. These waves form when a large and sudden displacement of water occurs, usually due to earthquakes below the surface of the ocean.
The force generated by the earthquake causes waves to radiate outwards in all directions and some cases, these waves can travel at speeds of up to 500 miles per hour which is as fast as a jet plane. At these speeds, tsunamis can travel hundreds to even thousands of miles before reaching the shore. Additionally, tsunamis have a very long wavelength from crest to crest which means if you are out on a ship you may not even notice one of these waves passing beneath you.