California is likely to bear some of the most significant impacts in the United States as an exceptionally strong El Niño develops in the Pacific, raising concerns about coastal flooding, heavy rain, mountain snow and damaging waves.

The last major benchmark for many Californians was the 1997-1998 “Super” El Niño. During that event, nearly a year’s worth of rain fell in downtown Los Angeles in February 1998 as powerful Pacific storms battered the state. Heavy rainfall triggered deadly landslides in Southern and Central California, while large waves damaged the coastline, including a section of the Santa Monica Pier.

Experts caution, however, that previous El Niño events cannot perfectly predict what will happen this time. The 2015-2016 Super El Niño, for example, brought considerably less rain to California than the 1997-1998 event.

The current El Niño is also unfolding alongside ongoing global warming, which could alter or intensify some of the weather and coastal impacts associated with the climate pattern.

California is nevertheless expected to be a major center of El Niño-related hazards in the United States. In September, Gov. Gavin Newsom declared a state of emergency to mobilize resources and prepare for potential impacts during the coming winter.

Among the biggest concerns are coastal flooding, heavy rain at lower elevations and increased snowfall in the mountains. Powerful Pacific storms could also generate larger waves, accelerating erosion along vulnerable sections of the California coastline and potentially disrupting important coastal transportation routes.

Scientists say California could experience record-high tide levels when the El Niño reaches its peak from late fall through winter. Coastal flooding is considered one of the more certain consequences of the event because El Niño can raise ocean levels on top of already rising seas caused by climate change.

Warmer-than-average tropical Pacific waters contribute to higher sea levels because warm water expands. Another factor involves Kelvin waves, large movements of ocean water that travel eastward along the equator before becoming trapped along the coast of the Americas and moving north and south.

These waves can raise coastal water levels by roughly six inches to one foot as they move northward. Satellite observations have already detected an area of elevated sea levels expanding northward from South and Central America toward the Baja California Peninsula.

The situation could be further complicated by an 18-year high-tide cycle, according to Patrick Barnard, research director at the Center for Coastal Climate Resilience at the University of California, Santa Cruz. The natural cycle could make King Tides higher than they otherwise would be.

Storm-generated waves are another concern. Barnard said studies have found that Pacific storms produce about 30% more wave energy during El Niño years than during years without the climate pattern. Some previous Super El Niño events produced increases of up to 50%.

Barnard estimated that the expected six-inch-to-one-foot increase in coastal water levels could expose an additional 170,000 people and $60 billion in property to coastal hazards compared with a non-Super El Niño year.

Experts say the coastal impacts are more predictable than the rainfall patterns. The exact path of Pacific storms remains uncertain, and previous El Niño events have affected different parts of California in different ways.

Dillon Amaya, a meteorologist at North Carolina State University, said strong El Niño events typically bring wetter-than-normal conditions to much of the American Southwest while the Pacific Northwest tends to be drier than normal. However, he cautioned that the relationship is not exact.

Heavy rain and mountain snow remain possible this winter, with studies showing that strong El Niño events are associated with above-average precipitation across California. If intense rainfall combines with stronger storm waves, the state could face flooding, mudslides and landslides.

The 1997-1998 Super El Niño provides an example of the potential damage. More than twice the average wet-season rainfall fell in the San Francisco Bay Area, while Central California experienced near-record precipitation. Flooding and mudslides caused deaths, while high coastal water levels and powerful waves damaged coastal communities.

Experts say the current event could produce different results because the climate has changed significantly since the previous Super El Niño events. Some effects could become more severe, while other expected impacts may not occur.

Amaya said the amount of heat beneath the surface of the tropical Pacific indicates that the current El Niño is on track to reach extraordinary intensity.

SOURCE: CNN, Andrew Freedman, updated September 22, 2026.