Safety First

HELEN AITKEN is a boating writer, photographer and former science educator from eastern North Carolina. She loves classic wooden boats, is an America’s Boating Club member and plays in the Intracoastal Waterway.

Wave Awareness

Know what to do if a seiche or meteotsunami occurs.

The Great Lakes is a region known for epic storms. Mother Nature makes life on the water more interesting with wave events called a seiche (“saysh”) and a meteotsunami (“meet-ē-o-tsu-na-mi”). These phenomena are wind-driven waves that are produced as storm fronts, storm lines and squalls move quickly with rapid changes in barometric pressure.

These waves bounce off the shore of enclosed or partially enclosed bodies of water like lakes, harbors, or rivers, and then continue to move until the energy has been depleted. With severe weather, a seiche or meteotsunami can be extremely dangerous and destructive in terms of property damage, erosion, injury and loss of life. Anyone visiting or living along the Great Lakes should be aware of these events and know what to do when they occur.

Seiches Seiche waves resemble water sloshing in a bathtub. Wind from strong storm lines pushes surface water to the most direct shore. The wave hits, it bounces off and returns through the waves moving forward. This may last for hours or days until the winds stop, the wave direction changes or the energy fades over time.

Every day, seiches occur mostly harmless and unnoticed, bringing deep-water nutrients to the surface for phytoplankton growth. Minor seiches may be confused with a tide, but there are no lunar/gravitational tides in the Great Lakes.

High winds and long storm lines create potentially dangerous seiche events, including rip currents, ice and snow floats, shoreline erosion and flooding. The National Weather Service and NOAA monitor the “slosh” and issue advisories for expected waves of 2 feet or more.

Historically, the deadliest seiches have occurred on Lake Michigan, yet Lake Erie has the largest seiches due to its shape, shallow depth and because it is situated in the direct line of powerful fall and winter storms. Even Niagara Falls stopped flowing temporarily because of a seiche.

Meteotsunamis This tsunami-type wave is not from an earthquake but rather fast-moving weather systems with dropping barometric pressures moving over a body of water. These waves match the speed of the weather system. Imagine 50 to 60 mph winds and waves.

Meteotsunamis become more dangerous in shallow water; the wave slows down, while the height and intensity increase, especially in semi-enclosed areas like a harbor. There, it hits, is deflected, and acts like the ball inside a pinball machine, traveling for hours long distances to other points. The first impact is the greatest, then the energy decreases as it’s deflected somewhere else. Eventually, the water returns to its origin without a sloshing effect.

Over 100 meteotsunamis occur yearly. Most are too small to notice, but large ones with unexpected high-water levels could flood shorelines, intensify rip currents and increase drownings. Large meteotsunamis occur about every 5 years.

Predicting waves The national weather service forecasts are based on radar imagery visualizing weather patterns, which helps predict possible seiche and meteotsunami events.

The NOAA’s National Ocean Service monitors over 50 instrument observation sites along the Great Lakes, which collect data every 6 seconds on wind, air temperature, relative humidity and barometric pressure. Site specific information is passed on and weather warnings are issued.

Seiche and meteotsunami safety • Leave your boat in storm-ready condition and secure things inside. • Check the weather forecast before boating, have a float plan, and keep your VHF radio and cell phone turned on. If a seiche warning is issued, leave the area. • Watch for rip currents, as these intensify from previous wave action. • Even when the storm is gone, these waves are unpredictable and can still appear. If you see the water is rising rapidly, get out of the water. • Kayakers and boaters should prepare for bad weather. Charge your cell phone, carry water, emergency food, appropriate clothing and shelter items in case of a stranding.

The Great Lakes are great, and so are the weather systems associated with them. The weather can suddenly change, and storms can produce seiche or meteotsunami wave events. Listen to the National Weather Service’s forecasts. Use common sense near and on the water, then share that information with others — it may save a life. ★