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Warmer fall predicted for LA as ‘blob’ settles off California coast

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Higher nighttime temperatures are in store

Gold and brown haze off a coastline with palm trees.
The big patch of warm water is nicknamed after a destructive marine heatwave that developed in 2013.

A massive “blob” of warm water is lurking off the California coast, and it could mean that Los Angeles won’t experience a true autumn. (Does it ever, though?)

UCLA climate scientist Daniel Swain says there’s a “high confidence” that temperatures will be warmer than average this fall. That’s partly due to an enormous new marine heat wave that has settled in off the West Coast, extending for more than 1,000 miles offshore, from Alaska to the southern tip of California.

The above average ocean temperatures could have perilous implications for marine life, and unless the water cools down quickly, they will also very likely contribute to higher air temperatures.

“Since we’re close to the ocean, if the ocean’s temperature is 2 or 4 or 6 degrees warmer than usual, the air will pick up more moisture and more heat, so it will be a little bit stickier and warmer,” says Art Miller, a research oceanographer at the Scripps Institution of Oceanography.

That will likely play out in the form of higher nighttime temperatures, not necessarily searing daytime heat waves, says Swain.

“Much of this temperature increase will come at night and on days that might otherwise have been ‘chilly’ or fall-like,” he says.

These maps show temperatures above normal in orange and red.

The big patch of warm water is being called the Northeast Pacific Marine Heatwave of 2019, but many forecasters are referring to it as a “blob,” a reference to a destructive marine heatwave that developed in 2013 in nearly the exact same place.

“It’s on a trajectory to be as strong as the prior event,” Andrew Leising, a research scientist at National Oceanic and Atmospheric Administration Fisheries’ Southwest Fisheries Science Center in La Jolla, says in a blog post on the center’s website.

The 2013 blob triggered long-lasting toxic algae blooms, depleted Chinook salmon populations, and caused hundreds of sea lions to starve. It lasted until December 2015.

Both blobs developed in much the same way: Winds that normally churn the sea, bringing cool water from deep depths to the surface—a process called upwelling—dissipated.

This new ocean heat wave is still relatively new and not as deep. Because it’s primarily affecting the upper layers of the ocean, there’s a chance it could break up quickly, according to NOAA.

But even if it doesn’t, Swain says a cool autumn is still probably not in the forecast. “The main predictive signal would just be the long-term warming trend in California,” he says.