Blob Watch: The Latest on the Northeast Pacific’s Unusual Warmth

A huge swath of ocean, extending from Hawaii to Baja California and north to the Alaskan coast, has been dominated for much of 2015 by unusually warm sea-surface temperatures (SSTs). In part of the North Pacific, the warm temperatures extend back more than two years. The region that’s come to be known as “The Blob” is more than just a fixed pool of warm water: it’s a dynamic entity that’s been shape-shifting throughout the last couple of years. Persistent as it’s been, The Blob may get a death blow this winter from El Niño.

What exactly is The Blob?
During the winter of 2013-14, researcher Nicholas Bond (University of Washington) noticed a large pool of unusually warm water based in the south central Gulf of Alaska. Within the topmost 300 feet of the ocean, temperatures were as much as 2.5°C (4.0°F) above average in February 2014. By springtime, this warmth had spread east to the coasts of Washington and Oregon. In a report to the Washington state climatologist, Bond dubbed the region of unusually warm water “The Blob.”


Figure 1. Sea-surface temperature anomalies (departures from average) for February 2014 compared to 1981 – 2010. The inner rectangle shows the area analyzed in Nick Bond’s 2015 GRL paper, straddling the region from 135°W to 150°W longitude and 40°N to 50°N longitude. Image credit: American Geophysical Union, used with permission from “Causes and impacts of the 2014 warm anomaly in the NE Pacific,” Geophysical Research Letters, Nicholas Bond et al., doi:10.1002/2015GL063306.


The Blob had its origins in the preceding winter of 2012-13, but Bond found its signature was considerably stronger in 2013-14. By late 2014, two other regions of warmth had developed, one in the Bering Sea and another in the subtropics off Baja California and Mexico. The Blob’s warm anomalies (departures from average) expanded further in 2015, spreading southward toward the equator while growing in east-west breadth. Meanwhile, El Niño began to generate its classic signature of warm water along the equatorial eastern Pacific, just south of The Blob, by the middle of the year. (See this loop of SST anomalies over the past 52 weeks, produced by NOAA’s Earth Systems Research Laboratory.)

The most recent analyses show that the original Blob is now part of a broader east-west zone of warmer-than-normal SSTs that extends west from the Aleutians to the Washington/British Columbia coast. Another zone of even greater warm anomalies runs across the subtropical Pacific from near Hawaii to the California/Mexico coast. Thirdly, along the equator, warmer-than-average SSTs prevail from the International Data Line to the South American coast. El Niño is clearly responsible for the band of equatorial warmth, and at least some of the subtropical warmth, which has fueled record-smashing hurricane activity across the Central Pacific. As for the higher-latitude Blob, that's another matter.


Figure 2. SST anomalies (departures from average) for the period from September 13, 2015 to October 10, 2015. The area analyzed in the inset box of Figure 1 is shown here as a black rectangle south of Alaska. Image credit: NOAA/ESRL/PSD Map Room.


What led to The Blob?
High surface pressure and light winds helped produce the original midlatitude Blob. The persistence of the high pressure at both surface and upper levels was dubbed the Ridiculously Resilient Ridge of 2013 in December of that year by Stanford University doctoral student Daniel Swain at his California Weather Blog. Like the Blob itself, the Ridge persisted as an identifiable feature during 2014 and 2015 as its location evolved. Swain also related the Ridge to the intensification of the ferocious multi-year drought that began in 2011 in California.

The Ridge and the Drought have close family ties. For the study area shown by the rectangle in Figure 1, Nick Bond found that the sea level pressure averaged from October 2013 through January 2014 was higher than for any Oct-Jan period since records began in 1949, and surface wind speeds were the second lowest on record. This relative lack of storminess reduced the amount of mixing between atmosphere and ocean and limited the amount of colder water flowing into the region from the north. In turn, this helped keep surface water over the Blob region from cooling as much as it usually would in autumn and early winter.

During the winter of 2014-15, storms continued to track far to the north across western Canada, again leaving the West Coast largely high and dry and allowing the Blob to gradually expand.

How exactly do the Blob and the Ridge relate to each other?
Experts tend to see the Blob and Ridge as closely connected, but likely triggered by something else. Here’s one leading explanation: back in July, we discussed a recent paper by Dennis Hartmann (University of Washington), who teased out apparent connections during the winter of 2013-14 between warm tropical SSTs west of the Date Line, the Ridiculously Resilient Ridge, and the cold, stormy conditions over parts of the Midwest and Northeast. Hartmann related this chain of events to the North Pacific Mode, a semi-cyclic pattern that helps explain multiyear variations in SSTs over the Pacific. Though many experts believe the tropical Pacific is the ultimate driver of the Ridge and Blob, others have pointed to potential higher-latitude involvement. Research by Jennifer Francis (Rutgers University) has examined the possible influence of Arctic sea ice on the Ridge and other “stuck” midlatitude weather features.

“The Blob and the Ridge most likely had a common etiology,” Swain told me in an email. “It's possible that, once present, the Blob exerted a reinforcing influence on the Ridge, and so there's some possibility that the presence of the Blob enhanced the resilience of the Ridge. But it seems pretty unlikely that the Blob itself was the cause of the Ridge, and so its presence or absence this year probably isn't very relevant for the kind of circulation pattern we are likely to see this winter.”

What happens to the Blob and Ridge this winter?
Strong El Niño events, like the one now in place, tend to generate big winter storms across the Northeast Pacific. Forecast models already show an intensifying parade of storm systems over the Aleutians and Gulf of Alaska for the latter half of October. Over time, the wind and waves from these and subsequent storms should act to erode the original midlatitude Blob. “I feel confident that a strong El Niño event will cool things in a large area around the Date Line and 40°N this winter,” Dennis Hartmann told me in an email. However, SSTs along the immediate coast from California to British Columbia may actually remain well above average this winter. That’s because powerful storms in the Northeast Pacific would tend to foster strong south winds near the coast. Waters near the surface tend to move to the right of the winds above (a process called Ekman transport), so the strong south winds would tend to push warmer water toward the coast and suppress any upwelling of cooler water.

The subtropical warm waters from Hawaii to California could take longer to scour out, as they’re partially a product of the El Niño that will likely remain in place through most or all of the winter. We can expect this southern blob-like feature to help provide warm, moist air for any Northeast Pacific storms that dive toward California. Figure 3 shows how this feature is considerably larger and stronger than it was during the similar El Niño event of late 1997.


Figure 3. Comparison of sea-surface height anomalies (departures from average) measured in late September 1997 (top) and 2015 (bottom), during the onset of comparably strong El Niño events. These images were created from data collected by the TOPEX/Poseidon (1997) and the OSTM/Jason-2 (2015) satellites, using space-based radar altimetry. High sea-surface heights indicate warmer-than-usual water. To create an apples-to-apples comparision, these images were processed by NASA to highlight the year-to-year signal, with seasonal signals and trends removed. Image credit: NASA/JPL.


“It's clear these warm waters have already been influencing weather conditions so far this summer (with an incredible number of Pacific hurricanes, including several that have recurved further northward than we've seen in years),” Swain pointed out. “Persistently warm to hot conditions--along with extremely high dewpoints and even some occasional thunderstorm-related downpours very uncharacteristic of the region--have been occurring across Southern California for months now.”

Swain added: “Ocean surface temperature anomalies of just a few degrees have the potential to add a lot of extra ‘juice’ to incoming Pacific storms this winter. That's yet another reason why it's important not to discount the increased risk of flooding this winter even as California approaches its fifth year since extreme drought began.” Another big question mark is whether any storms that sweep as far north as central California will dump more rain than snow over the Sierra Nevada, where snowpack storage is crucial for the next year’s water supply in California.

Nick Bond is already looking further ahead. “The big question, in my mind, is what happens after the upcoming winter,” Bond said in an email. “Will the weather/wind patterns favor a continuation of the warm ocean conditions, or will there be a switch back to patterns associated with cooler NE Pacific waters?” Recent long-range models suggest that a La Niña could begin emerging in the wake of the current El Niño by mid-2016. If so, that would have a cooling effect on the waters off the U.S. West Coast. Countering this would be any persistence of the Pacific Decadal Oscillation, which entered an apparent warm phase in early 2014. Once it’s in place, a given PDO phase can predominate for more than 20 years, and a warm PDO tends to support warmer-than-usual waters off the U.S. West Coast. Added to all this is the overall long-term warming of both atmosphere and ocean across the planet, which has spiked measurably over the last couple of years (partly due to El Niño).


Figure 4. Ocean sunfish have been observed in both 2014 and 2015 off the southern Alaska coast, hundreds of miles north of their usual habitat. The heaviest bony fish in the world, ocean sunfish prefer waters of 54°F or warmer. Crews from the Alaska Fisheries Science Center caught the large ocean sunfish pictured here. Image credit: AFSC, via NOAA.

The Blob, El Niño, and marine life
Bond noted that any prolonging of the unusual oceanic warmth off the West Coast could have major impacts on native marine ecosystems. Many marine species shift north with El Niño and south with La Niña, but those events typically last just a year or two; the Ridge and Blob have now been in place for more than two years. In breadth and strength, the warming in the North Pacific over the last three years has been the most prolonged since records began in 1900. “Many species can shrug off a bad year or two, but longer runs have greater impacts,” said Bond.

"This El Niño is liable to bring some really strange changes in ocean conditions because the widespread warming of the North Pacific we saw with the blob was so far outside of our experience," said Northwest Fisheries Science Center oceanographer Bill Peterson in a NOAA feature story this month. "When you put an El Niño on top of that it is anyone's guess as to how this will affect marine organisms."

We’ll cover NOAA’s official winter outlook for 2014-15 after its release on Thursday. For a deeper dive into the Blob, check out the excellent article by Eric Simons published last month in Bay Nature. If you prefer your Blobology 101 in cartoon form, below is a fun animation produced by Southern California Public Radio (KPCC); h/t to wunderground member barbamz.

Bob Henson