El Niño 2015 sets new heat record. Here's what it means

Wednesday, November 18, 2015, 4:31 PM - El Niño set a new record for heat in the central Pacific Ocean this week. Is it on track to become the strongest El Niño we've ever seen, and what could this mean for the winter to come?

So far, El Niño 2015 has been very unusual. Teasing NOAA forecasters with signs and signals through 2014, it ultimately procrastinated in its actual development until early 2015 and it has been growing since, into a rival for some of the strongest El Niños we have on record.

As of now, it has already set a new record, though. Weekly measurements of temperatures in the central Pacific ocean are now 3.0 degrees Celsius above normal for the very first time in the quarter century that these measurements have been taken.

The animation below, provided by US National Oceanic and Atmospheric Administration's Climate Prediction Center, shows the past 12 weeks of Pacific Ocean sea surface temperature anomalies.

In tracking ENSO - the El Niño Southern Oscillation - forecasters divide the equatorial Pacific Ocean into four regions. The Niño 1 and Niño 2 regions (collectively Niño 1+2) lie just south of the equator, along the west coast of Ecuador and Peru, and extend out to 90W longitude. The other regions straddle the equator, with Niño 3 covering from 90W to 150W and Niño 4 from 150W to 160E longitudes.

One last region, known as the Oceanic Niño Index (ONI) or Niño 3.4 region, covers the central equatorial Pacific, from 120W to 170W. It is this region that forecasters use when tracking ENSO and comparing the strengths of the patterns that develop from year to year.

Overlaying these regions on the November 11 panel from the animation (above) shows how the 3.0 degree C "core" of the current temperature anomaly pattern stretches right across ONI/Niño 3.4 for that week. 

According to NOAA's records, temperature anomalies in other regions of the Pacific have certainly reached 3.0 degrees C or higher in the past 25 years, notably:

• From May 1997 to February 1998 and April 1998 to June 1998, in the Niño 1+2 region, with a peak of 4.6 degrees C above normal in August 1997

• From September 1997 to February 1998 in the Niño 3 region, with a peak of 3.7 degrees C above normal in November 1997

At the same time as this November 1997 Niño 3 region peak, temperature anomalies across the Niño 3.4 region got up to 2.8 degrees C, which was the highest temperature departure on record in that region until now.

Impressive? Significant? What does this mean?

Reaching a new temperature record like this is certainly interesting and noteworthy. What does it tell us, though?

With regards to this year's pattern, on the whole, not that much.

Back in July, NOAA Climate Prediction Center meteorologist Michelle L'Heureux stated the reason for this quite succinctly when she wrote on Climate.gov's ENSO blog:

"While a short-term (daily or weekly) number might be striking, it shouldn’t be used as an indicator of El Niño strength unless it is carefully placed into a larger context."

Weekly averages in the central Pacific have been on the rise since the beginning of September. This does give us an indication of how quickly the pattern is growing. However, watch all the bumps and wiggles in the short-term data and you'll see the index rise and fall, even during the strongest events. 

NOAA forecasters smooth out all the rises and falls in the short-term values by setting the Oceanic Niño Index (ONI) as a three-month average. Currently, the latest ONI value (from August-September-October), puts the current El Niño at 1.7 degrees C above normal. This is far from the highest value ONI has reached for an El Nino. That would be the ONI values of 2.3 degrees C above normal, which were seen at the end of 1997.

So, regardless of how the impressive the weekly values look...

they simply don't tell the whole story.

"It's certainly impressive that the weekly got to 3 degrees Celsius," said Tom Di Liberto, a meteorologist at NOAA's Climate Prediction Center, according to Mashable. "But we've been trying to say that we don't know if this is a blip or a longer-term pattern. Just because we had a week at this level doesn't necessarily mean that this is the strength of this El Niño."

El Niño 2015 backing off?

There's been one very noticeable shift in El Niño over the past few months. At the same time that temperatures anomalies closer to the central Pacific have been getting larger, anomalies measured in the waters off the coast of Ecuador and Peru have actually dropped by nearly a full degree Celsius.

Since the strength of El Nino is ranked based on central Pacific temperature anomalies, the expectation is that the next three month ONI value (September-October-November) will still jump significantly, likely to +2.0 or higher. Also, since these values are longer-term averages, the anomalies already seen in October and November may keep the ONI value at record or near-record levels until the end of the year.

Still, while too much can be read into the weekly values on their own, the longer-term trend seen in the eastern part of the equatorial Pacific may indicate something fairly significant is happening to this El Niño pattern.

"There are signs that the current El Niño is peaking at this time and will steadily weaken as we progress through the winter," says The Weather Network's Dr. Doug Gillham.

Global temperature patterns are quite different this year than they were in 1997-98, says Gillham, even looking beyond the equatorial Pacific. This already changes up what we might expect from an El Niño winter, but additionally, this potential shift in where the excess heat from El Niño is located may result in something entirely different.

"While El Niño will still have a major influence on our winter weather patterns, the nature of impacts for a weakening El Niño are different from that of an El Niño event that is strengthening through the winter," says Gillham.

What will this mean for winter 2015/16 across Canada? Check out our Winter Preview for a first look ahead of our official Winter Outlook, which is due out at the end of November.

Sources: NOAA | Climate.gov | Mashable

Related Video: Understanding El Niño