When viewing weather radar, people are used to seeing “ground clutter” — the radar beam’s energy striking the ground or buildings or other features and scattering some of the energy back to the radar. But what are the echoes south of the Island of Kauai?
Answer: Wave clutter.
Just like the earth is not flat, often neither is the ocean. In the case the radar’s energy (red) strikes the tall wave and part of it (purple) reflects back to the radar. It is displayed as wave clutter. Of course, in nearly calm seas there is little, if any, clutter from waves.