A massive pool of warm water moving toward the West Coast could raise sea levels and worsen flooding in California this winter as a powerful El Niño continues to strengthen, scientists say. The phenomenon, called a Kelvin wave, is not a breaking wave like those seen at a beach. It is a planetary-scale movement of warm water that travels east along the equator after the trade winds weaken, said Michael Wysession, a professor of geophysics at Washington University in St. Louis.