The Blob is Back: Anomalous Warmth Returns to the North Pacific Ocean

Jonathan Belles
Published: September 21,2016
The warm pool of water in the northern Pacific that is known as 'The Blob' is back, and it could change the weather on the West Coast if it sticks around.
The history of the blob goes back to late 2013 and 2014, when it contributed to changing downwind weather patterns that winter and had impacts on ecological and marine life in the North Pacific Ocean and in the Pacific Northwest.

What is 'The Blob?'

It is an area of substantially warmer-than-average water temperatures in the northern Pacific Ocean off the coast of Alaska.

Anomalous ocean temperatures compared to 1981-2010. Warmer than average ocean temperatures are in red and orange.

Just in the last month or so, warmer ocean temperature anomalies have reappeared.
Some of this signal can be attributed to the recent warm phase of the Pacific Decadal Oscillation (PDO), which has been in play since 2014.
The warm phase of the PDO is associated with a horseshoe-shaped warmer than average pool of water stretching from the Gulf of Alaska and the northern Pacific southward to the West Coast of the United States and southwestward into the the equatorial region of the central Pacific.
As you can see from the map above, this is not the classic warm PDO. The signal for the recent mini-PDO spike is waning, and slightly cooler-than-average ocean temperatures along the Equator have been common in recent months.
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So if it isn't entirely the PDO's fault, what else is contibuting to the warm signal?
Since June 2016, a large contributor to The Blob is that surface pressure has been anomalously high in the Pacific between Alaska and Hawaii according to a blog by University of Washington atmospheric scientist Dr. Cliff Mass.

Figuring out whether the ridge caused the Blob or if the Blob caused the ridge can be tough to do according to Daniel Swain, a NatureNet Postdoctoral Fellow in the Institute of the Environment and Sustainability at the University of California.
There is evidence, though, that the ridge, or area of high pressure, is in control.
Areas of high pressure are associated with sinking air that warms as it sinks. Over water, high pressure systems that get stuck or are frequently in place like this area take time to warm the water below it up. In the United States (over land), these high pressure systems are responsible for heat waves, or just prolonged periods of peaceful weather.
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High pressure systems also generally have less wind near the ground or ocean surface, which slows down the mixing of the ocean's surface and allows the temperature of the top layer of the ocean to remain higher.
Since this ridge has been in place since mid-summer, it also will act to trap warmth in place until it dissipates. Remember that we are looking at anomalies or departures from what we would expect, and not actual temperatures. Actual temperatures are running in the 60s and 70s (or low to mid-20s in Celsius).

What Does This Mean in the United States?

In 2013 and 2014, this pattern brought more warm-water species of marine life in the Pacific and led to a large shake up of the food chain on the U.S. West Coast.
The pattern brought dry conditions along the coast between Juneau, Alaska and San Diego, California. California saw its driest year on record in 2013.
Temperatures were also warmer than average during the fall and winter in the Southwest, but were significantly cooler during that time period in the central U.S. and along the East Coast. While California, Nevada, and Arizona had their warmest year on record in 2014, parts of the Mississippi Valley had one of their top 10 coolest years in 2014.
As for the forecast going into late 2016, if the pattern stays the same, weather-makers such as low-pressure systems will be forced swing southward at a more eastward point in the U.S.
In other words, the West Coast would be on track for a slightly drier and slightly warmer autumn.
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In Alaska, this would generally mean a wetter than average winter would be in store since low-pressure systems would be directed north of the blob and through Alaska.
We should note that the blob is not the only atmospheric player in this game and that this forecast can and will change.
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