NOAA explains what Kelvin waves are

NOAA published an explanation of Kelvin waves on October 14, 2026. The waves are slow-moving, relatively flat, warm water waves that stretch thousands of miles across the Pacific Ocean. They move at about five to ten miles per hour and can take about two to three months to cross the Pacific Ocean before reaching the South American coast.

The waves affect the upper surface of the equatorial ocean between the surface and the thermocline at depths between 660 and 3,300 feet. They can raise sea level by about 6 to 12 inches or more due to the larger volume of warm water occupying more space than colder water.

Kelvin waves form along the equator in the western Pacific Ocean and travel west to east in response to the weakening of the trade winds during El Niño. When they reach the South American coast along the equator, the wave splits. About half of the wave heads south toward the pole and the other half heads north along the west coast of the Americas.

The announcement said satellite radar altimetry measurements reveal the sea surface signature of Kelvin waves where the ocean surface is higher or lower than its long-term average. Yellow color represents elevated sea surface heights at ranges of 0 to 0.25 meters. Red or orange color represents elevated sea surface heights at ranges of 0.25 to at least 1 meter.

The announcement said Kelvin waves are difficult to see with the naked eye as they are large in scale, slow moving and do not break onshore like typical ocean waves. Typical ocean waves move at speeds averaging 20 miles per hour with wavelengths between 10 to 100 feet.