Sea surface temperature difference from normal, November 3 (NOAA)

The waters along the west coast of North America, from Baja California in Mexico to the Gulf of Alaska, are warmer than they’ve been in decades.  They may portend more drought for the West Coast this winter, and cold, stormy conditions in the East.

The plume of warm water bleeding up the coast is nothing short of historic.

Writes the Seattle Times:

“The North Pacific hasn’t been this warm ever, as far as anyone knows. It’s really strange,” said Bill Peterson, oceanographer with NOAA’s Northwest Fisheries Science Center in Newport, Ore. “It looks like an El Niño, but it really isn’t. We don’t really know what it is.”

Adds the Alaska Dispatch News:

“This is the warmest we’ve seen in 17 years. We believe that to be significant,” said Russell Hopcroft, a professor at the University of Alaska Fairbanks School of Fisheries and Ocean Sciences and chief scientist for the long-term monitoring program.

And the San Jose Mercury News says the water in parts of Central and Southern California is warm enough for a swim:

Temperatures off the California coast are currently 5 to 6 degrees Fahrenheit warmer than historic averages for this time of year — among the warmest autumn conditions of any time in the past 30 years.

“It’s not bathtub temperature,” said Nate Mantua, a research scientist with the National Marine Fisheries Service in Santa Cruz, “but it is swimmable on a sunny day.”

Marine biologists are stunned by an onslaught of outsider species up and down the West Coast.  Among those spotted? A live ocean sunfish and warm-water blue shark in the Gulf of Alaska, mahi mahi off the coast of Oregon, a Pacific sea turtle common in the Galapagos near San Francisco, and marlin in the waters off Southern California, not to mention many others.

A likely contributor to the warmth is the high pressure (or ridging) pattern over the western U.S. this year. In this pattern, winds from the south push warm water eastward, allowing it to converge along the coast. More commonly, winds from the north hold warm waters in the tropics and produce upwelling which brings cold deep water towards the surface.

So what do the warm coastal waters mean for the weather along the West Coast and downwind towards the central U.S. and, ultimately, East Coast as we head into winter?

Often, warm waters off the West Coast are complemented by a ridge or bump in the jet stream, leading to warmer than normal and drier than normal weather in the western states. Indeed, this ridging pattern has persisted for over a year, enhancing the West Coast drought. Some have dubbed it the “ridiculously resilient ridge.”

Like a see-saw, the ridge in the West tends to buckle in the East, digging out a trough or dip, that favors colder and sometimes stormier than normal conditions.

Capital Weather Gang’s Matt Rogers, who specializes in long-range forecasting, said the warm waters off the West Coast don’t necessarily establish the pattern, but assist in holding it in place. “It’s not a pattern driver, but once you get a ridge in the West, [the warm water] it helps it stay there longer than it normally would,” he said.

Major shifts in the atmospheric flow can certainly disrupt this pattern, Rogers said, but “if you have the pattern in the front door of winter, it’s more likely you’ll keep it there.” For this reason, Rogers favors a continuation of the drought in the West this winter, and cold, inclement weather in the East. The warm Pacific waters may, however, facilitate some drought relief in Southern California by enhancing the tropical moisture feed from Pacific into the southern U.S., Rogers said.