Kelvin waves are difficult to see with the naked eye as they are large in scale, slow moving and don't break onshore like typical ocean waves. In this graphic, 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. The yellow color represents elevated sea surface heights at ranges of 0 to 0.25 meters (0 to 10 inches). The red/orange color represents elevated sea surface heights at ranges of 0.25 to at least 1 meter (10 inches to at least 40 inches). Data: NOAA/NESDIS Center for Satellite Applications and Research; visualization: NOAA CoastWatch, Oct 7, 2026.

Kelvin waves are slow-moving, relatively flat, warm water waves that stretch thousands of miles across the Pacific Ocean. These waves affect the upper surface of the equatorial ocean — between the surface and the deeper thermocline (the transition layer below the surface where temperatures get colder) at depths between 660 and 3,300 feet.…