An intense marine heat wave has California in its crosshairs, with impacts set for land and sea

By Andrew Freedman, CNN

(CNN) — Something unusual and with far-reaching consequences is lurking in the sea off the California coast, stretching all the way down the Baja Peninsula and more than 500 miles to the southwest.

In this broad region, a large, long-lasting and record-setting marine heat wave has set in and is forecast to persist and intensify, altering the weather conditions on the West Coast and adversely affecting the marine food chain.

This heat wave, which is the oceanic equivalent of a heat wave on land, could have broad ramifications for sea life, as warm water species like hammerhead sharks and bluefin tuna migrate into areas where they are normally not seen, and cold-water species move deeper and further north.

The marine heat wave may have widespread impacts on the weather in the West, making off-the-chart heatwaves like March’s more likely and intense, supercharging rainfall and even allowing tropical systems to come northward into California.

Scientists at Scripps Institution of Oceanography are monitoring ocean temperatures along the California coast, where their records stretch back more than a century. They have been recording one hot ocean record after another, especially during the past few weeks.

Since January 1 and through the end of last week, there were 36 days when sea surface temperatures at Scripps Pier in La Jolla, California set records for the hottest water temperature ever recorded on that date. This is significant, since daily data at that location goes all the way back to 1916.

Scripps’ scientists are using robotic ocean-going vehicles to investigate water temperatures below the sea surface. They have found that the unusually hot waters extend to deep depths and are comparable to conditions typically seen when a significant El Niño has taken hold.

El Niño features unusually hot ocean waters near the equator in the Pacific Ocean, along with significant changes to global weather patterns and the planet’s climate.

However, while a potentially strong El Niño is predicted to develop by the end of the summer to early fall, there is not one present right now. This warns of just how much hotter water temperatures could get in this region during the coming weeks and months.

According to Dillon Amaya, a research scientist at the National Oceanic and Atmospheric Administration, a climate cycle that is a precursor to El Niño now joins the distinct California marine heat wave with a far bigger area of unusually hot ocean waters that extends all the way to Indonesia. (The climate cycle is known as the Pacific Meridional Mode.)

Together, these two entities comprise one of the biggest marine heat waves on Earth right now.

Computer model projections show this broad hotter-than-average region morphing into an El Niño along the equator over time, while the smaller, closer-in marine heat wave continues to bake the waters off the California coast, potentially even into the fall and winter months, Amaya said.

The California marine heat wave is already having an impact on the Pacific Ocean’s food web. Tammy Russell, a marine ornithologist at Scripps, said that seabirds in particular are being impacted, which is a warning sign about more serious impacts to come for other species as well. Russell studies seabirds closely, and how they interact with the broader marine ecosystem.

“We have been seeing an increase in the number of seabirds coming into rehabilitation facilities and washing up dead on the beaches across southern and central California for a few months now,” she said in a statement. “Most of the birds are emaciated and have tested negative for HPAI (avian flu), therefore, we have concluded that the primary cause of this mortality event is due to starvation.”

With cold water fish moving northward and to deeper depths, seabirds may be having difficulty locating their typical food sources, Russell said. There has been an increase in the number of struggling Brown Pelicans, Brandt’s Cormorants and Common Murres appearing up and down the coast all the way to San Diego, she said.

The marine heat wave is especially intense from the Pacific coast of Mexico north into Southern California and all the way up to San Francisco, with sea surface temperatures running four degrees Celsius, or about 7.2 degrees Fahrenheit, above average in many areas. This is an “astounding” magnitude for a marine heat wave, Amaya said.

He traced the heat wave’s origins to the same high-pressure area that led to a record-breaking heat wave across the West during March and into April. That weather feature led to unusually light surface winds off the coast and caused marine clouds to be less abundant, allowing ocean water temperatures to spike as they absorbed more of the sun’s energy, Amaya said.

“You don’t get a marine heat wave of this magnitude or spatial extent without some sort of atmospheric driver,” he said, pinpointing the Western ridge of high pressure as the culprit. He added that other factors, including El Niño, are likely to keep it going for many months to come.

Human-driven climate change caused by the buildup of climate pollution in the atmosphere is a major factor behind the increased prevalence and intensity of marine heat waves in recent years.

“Every marine heat wave is going to be warmer than the last because of global warming,” Amaya said.

According to climate scientist Daniel Swain of the University of California’s Agriculture and Natural Resources, the heat wave is already altering California’s weather conditions and could have significant ramifications for the months ahead.

For example, the presence of warmer than average water lurking along the shore could make more humid heat waves over land this summer.

Humid heat is something many Californians are not accustomed to, Amaya said.

The elevated water temperatures could even make California more vulnerable to tropical cyclones.

Typically, cold ocean waters near California prevent East Pacific tropical storms and hurricanes from threatening the state. But that could change this summer as the hotter waters make it easier for a storm, or its remnants, to strike Southern California, Amaya said.

One recent storm to bring significant impacts to Southern California was Tropical Storm Hilary in 2023, which caused flooding as its moisture swept inland.

The bottom line is that this heat wave, with all its effects across land and sea, is here to stay, both Swain and Amaya emphasized.

“Boy howdy does it look like it’s going to be a persistent and extreme marine heat wave into the summer,” Swain said.

The-CNN-Wire
™ & © 2026 Cable News Network, Inc., a Warner Bros. Discovery Company. All rights reserved.