Seeing the Pacific act like it’s August while standing on a pier in mid-May has a peculiar quality. The numbers below reveal a different picture, even though the water off northern California still has the typical grey-green sheen this time of year. The agency’s own marine heatwave alert system, which was developed in 2019 to monitor precisely this kind of thing, is now being asked to interpret something it was never quite intended for. NOAA‘s satellites have been detecting an exceptionally warm sheet of ocean that just won’t go away.
The northeast Pacific reached an average surface temperature of 20.6°C on September 9, 2025, marking the peak of the current heatwave, which is somewhat clinically named NEP25A. The heatwave began last summer. That is the highest value ever recorded for the area. Scientists predicted that the warm water would weaken, move away from the coast, and gradually fade by late autumn. It did become weaker. Then it returned. After eight months, it now covers a triangle of ocean from Hawaii to British Columbia and down toward Mexico, spanning halfway across the Pacific.
Running the California Current Marine Heatwave Tracker from NOAA’s Southwest Fisheries Science Center, Andrew Leising has enough experience to know what is out of the ordinary. The previous benchmark was “The Blob” of 2013–2016, a marine heatwave that caused so much disruption that it became one of the few terms related to oceanography that were used in regular news. According to Leising, the new event is comparable to The Blob. Strangely, it’s not just its size that makes it unique. The timing is the issue. These waters were expected to remain colder due to La Niña conditions. They didn’t.
You get the impression that the alert system itself is now a part of the narrative when you are inside NOAA’s offices. Since the first global forecasts were published in Nature around 2022, marine heatwave forecasting has only been operational. The technology was specifically designed to prevent resource managers, fishing fleets, and coastal communities from being unprepared for another Blob. However, the system was essentially trained on historical occurrences that, despite their severity, followed a pattern. NEP25A does not completely.
University of Arizona atmospheric scientist Kim Wood recently wrote that she was “out of superlatives” after reviewing the most recent data. When a working scientist makes such a remark, it usually has some significance. At the height of hurricane season, sea surface temperatures in the eastern Pacific are currently higher than they typically would be. According to NOAA’s own forecast, which was published last week, the heatwave is expected to intensify and spread throughout the summer rather than abate, potentially merging with an emerging El Niño in ways that forecasters are still attempting to model.
Even though they haven’t made headlines yet, the downstream effects are already apparent. In Wyoming, Utah, Colorado, and New Mexico, snowpack has virtually disappeared, with a record low this year. Over one-third of U.S. weather stations broke all-time temperature records in March, a percentage not seen since the Dust Bowl. Climatologist Larry O’Neill of Oregon State is concerned that dry thunderstorms could start wildfires in an already water-scarce landscape. This is not a coincidence.
The effects of the warm water on the organisms that inhabit it are another issue. The most recent significant heatwave delayed the Dungeness crab fishery, killed sea lion pups, entangled humpback whales, and drove market squid northward. Some of that damage has been avoided because NEP25A hasn’t yet pushed as far into the water column or hugged the coast as firmly. However, last fall, unusual numbers of tunas were caught off the coast of Alaska, which is the kind of minor anecdotal detail that usually indicates a larger story is developing beneath the surface.
It’s difficult to ignore the fact that the very instrument designed to foresee these occurrences is now discovering its own limitations in real time. The next few months will begin to reveal whether the ocean continues to write chapters faster than anyone can read them or whether the system detects what comes next.
