Pacific Marine Heat Wave Persists as El Niño Watch Issued

A marine heat wave identified as NEP25A has remained widespread across the Northeast Pacific through spring 2026, with coastal sea surface temperatures off California among the highest recorded for this time of year. The system reached a record size of about 10 million square kilometers in September 2025 before contracting and then re-intensifying along the coast in December, according to National Oceanic and Atmospheric Administration analyses published in April.

NOAA classifies the climate system as ENSO-neutral as of April, with an El Niño watch in place for later in 2026. Forecast models indicate marine heat wave conditions are likely to persist through spring and summer offshore. Scientists note that strong seasonal upwelling of cool, nutrient-rich water could limit some coastal impacts, as occurred in 2025.

Comparison to 2014-2016 Event The 2014-2016 period combined a large marine heat wave known as the Blob with one of the strongest El Niño events on record. That combination reduced forage fish abundance and contributed to the starvation of seabirds and marine mammals.

More than half of Alaska's roughly 8 million common murres disappeared between 2014 and 2016, and an estimated 62,000 murre carcasses washed ashore from California to Alaska, according to NOAA. Researchers concluded most birds starved after warming waters disrupted the marine food web.

Young California sea lions also experienced increased strandings when prey moved farther offshore or deeper, the National Park Service reported.

expects El Niño to strengthen into a moderate or strong event by fall. Researchers state that the current marine heat wave has not matched the Blob in duration or intensity, and widespread ecological impacts have not yet been documented.