A mass of warm water is moving toward the southern coast of California in an oceanic phenomenon known as a “Kelvin wave.” Researchers expect its effects to reach San Francisco in about three weeks. This is occurring alongside a strong El Niño, which is expected, according to the source, to be the largest in about 1,000 years, increasing the risks of storms, higher waves, and coastal flooding during the winter.
A Kelvin wave forms when the trade winds that normally push warm water from the tropical region of the Pacific Ocean toward Australia and Southeast Asia weaken. As the winds change direction or calm, the accumulated water moves eastward toward the coasts of South America and then splits northward and southward when it encounters land. Part of this movement reaches the western coast of the United States.
What could change on the West Coast?
Researchers expect the warm water to raise sea levels along the West Coast by 6 to 12 inches. This rise is relatively temporary and linked to the wave, but it is added to a long-term rise of about 8 inches over the past century, increasing the exposure of low-lying areas to inundation.
The wave’s effects may also continue through the winter and into the beginning of the following year, with the possibility of increased rainfall and winter storms. A Kelvin wave does not produce surface waves that break like ordinary beach waves; instead, it raises water levels and increases the energy available to storms when they reach the coast.
Why does the timing of storms matter?
Damage increases when storms coincide with the highest tide levels. Kate Huckelbridge, chair of the California Coastal Commission, explained in a memorandum that storms peaking during high tide are more likely to cause damage than the same storms during low tide. Therefore, the level of risk depends not only on the storm’s strength, but also on its coincidence with the tide and elevated sea levels.
Nate Mantua, a researcher at the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center, said that some effects can be forecast, but not all of them. El Niño seasons in the North Pacific Ocean typically increase the number of storms and wave heights, which, when added to the elevated sea level, could lead to more inundation and expose coastal areas to ocean energy.
Limitations and what needs to be monitored
Kelvin waves are a natural phenomenon known for thousands of years, and NOAA has tracked them since the beginning of ocean-data recording. However, the source links their current danger to the long-term rise in sea level and the expected strength of El Niño. The material does not establish that every local effect will occur to the same degree; the intensity and paths of storms, as well as the timing of the tide, remain factors that determine the actual outcome.
The significance of the development lies in showing how a large-scale oceanic change can become a direct local risk, particularly in low-lying coastal areas. The open question is the extent to which the temporary rise in sea level will coincide with the strongest storms and high tide during the winter season.