A series of warm-water pulses moving up the West Coast is expected to raise coastal water levels in Oregon and Washington by roughly 6 to 12 inches, adding to winter risks from high tides, storms and large waves. The pulses, known as Kelvin waves, were expected to move north along California at about 150 miles a day beginning in early October, according to ocean researchers. More could arrive from October through February as a strong El Niño develops. The waves do not arrive like tsunamis or break on shore. They are broad, moving bulges in the ocean that raise the background sea level. That higher baseline can make storm surges and unusually high tides more consequential, said Michael Jacox, a research oceanographer with the National Oceanic and Atmospheric Administration. The added water is not expected to cause flooding by itself. But it can compound existing coastal hazards, including erosion and damage to beaches, homes and infrastructure. Large North Pacific swells and spring tides expected during the El Niño season could increase those risks, said Sean Vitousek, a research oceanographer with the U.S. Geological Survey. Past major El Niño events, including those in 1982-83, 1997-98 and 2015-16, brought some of the West Coast’s most severe beach erosion on record, Vitousek said. Losing protective beaches can leave coastal property and infrastructure more exposed to waves and flooding. Kelvin waves form when equatorial trade winds weaken or reverse, allowing warm water normally pushed west across the Pacific to move east toward South America. From there, the water can travel north and south along the American coastline. Researchers said one such wave passed through in May or June, and another may be forming. Washington state Department of Natural Resources staff are monitoring the situation and coordinate regularly with the state Emergency Management Division, spokesperson Courtney James said. The agency had not been asked to take special preparatory measures as of early October. California has declared a state of emergency to prepare for the expected El Niño season. In Orange County, officials said they were placing emergency sand on beaches as quickly as possible amid existing damage from recent swells. Conditions there illustrate how higher water levels could add pressure to already vulnerable coastlines. The eventual damage will depend on the strength and timing of storms and tides, researchers said. While it is too early to know whether the coming winter will set records, scientists say the developing El Niño could become one of the strongest observed.