Marine heat wave raises ocean temperatures off California coast

Coastal sea surface temperatures are among the highest ever recorded for this time of year. NOAA's April analyses show large portions of the U.S. West Coast, particularly off California, remain affected. The event has at times rivaled the 2014-2016 heat wave in spatial extent but has not matched it in duration or depth of warming.

Forecast models indicate conditions are likely to persist through spring and summer, with an increasing chance of coastal warming as the region may transition toward El Niño later in 2026. As of April, NOAA classifies the climate system as ENSO-neutral with an El Niño watch in place for later in the year.

Additional effects Harmful algal blooms can form in the warm, slow-moving water, sometimes producing toxins that lead to beach advisories or temporary closures. Shifting conditions have also resulted in more frequent reports of jellyfish and other stinging organisms in some areas.

Fish species often move deeper or farther offshore in search of cooler water. Shellfish harvesting can be disrupted during toxic bloom events, prompting temporary fishing restrictions. These changes can affect seafood availability and pricing across California.

A marine heat wave is defined by the National Oceanic and Atmospheric Administration as a period of unusually warm ocean temperatures lasting days, weeks or months. These events are driven by shifts in ocean currents, persistent weather patterns and larger climate systems such as El Niño.

Oceans have absorbed about 90 percent of the Earth's excess heat energy over the past 50 years. In March, ocean waters along parts of the West Coast were about 3 to 4 degrees above normal. Each of the past nine years has set a new record for ocean heat content.