Record-Tying Strong El Niño 2015-16 May Finally Have Fizzled

Jon Erdman
Published: May 24,2016
The El Niño of 2015-16 may have finally dissipated, according to just-released data from NOAA.
Sea-surface temperature anomalies in the so-called Niño 3.4 region of the central and eastern equatorial Pacific Ocean dipped below the +0.5 degree Celsius El Niño threshold the week of May 15-21, after three-month running mean anomalies tied the record for the strongest El Niño this past winter.
El Niño, the periodic warming of the equatorial eastern and central Pacific Ocean, can shift weather patterns over a period of months, bringing the possibility of more sustained warm, cold, wet or dry weather in parts of the world.
The rapid weakening of this strong El Niño this late winter and spring was quite dramatic, with positive surface anomalies virtually vanishing in about 3.5 months' time since the week of Groundhog Day, according to NOAA's Climate Prediction Center.
The May 15-21 weekly anomaly of only +0.2˚C was the lowest positive anomaly in the Niño 3.4 region since the week of Aug. 13, 2014.

Weekly SST anomalies (degrees Celsius) from January 31 through May 21, 2016. The cooling of equatorial Pacific Ocean surface temperatures, indicative of the weakening El Niño, is highlighted.

Australia's Bureau of Meteorology declared El Niño finished on May 24, citing both cooling sea-surface temperatures, as well as atmospheric indicators such as stronger trade winds (the easterly winds near the equator) and diminished cloudiness (showers) near the International Date Line over the past few months.
In an eye-catching NOAA animation released in mid-May, you could see the colder-than-average water swarming eastward across the International Date Line, eating away at the warmer-than-average equatorial Pacific water from below.

Animation illustrating the advance of cooler-than-average water in the equatorial Pacific Ocean from mid-March to early May 2016, eroding what had been a strong El Niño.

For bookkeeping purposes, NOAA typically uses the three-month running mean anomalies to define the beginning and end of El Niño and its opposite, La Niña. Think of this as somewhat similar to how economists wait to define a recession until sometime after it actually began or ended.
NOAA declared the El Niño had begun during the Feb.-April 2015 period.
El Niño and La Niña events typically only last for nine to 12 months, and typically recur again every two to seven years, according to Columbia University's International Research Institute for Climate and Society.
(MORE: A Tale of Two El Niños ... What Made This One Different?)
At any rate, these trends suggest La Niña, the periodic cooling of equatorial Pacific Ocean water, is increasingly likely by late summer or fall, consistent with the large majority of model forecasts. A couple of ensemble forecasts even have a strong La Niña forecasted by late summer or fall.

Ensemble model forecasts of SST anomalies in the Niño 3.4 region from April to December 2016, showing the potential La Niña developing by summer 2016.

Both NOAA's Climate Prediction Center and Australia's Bureau of Meteorology issued a "La Niña watch," indicating La Niña may develop within the next six months. NOAA/CPC places the odds of La Niña conditions by late summer at over 60 percent, increasing to over a 75 percent likelihood by late fall.
Flip-flops from a strong El Niño to La Niña are not unusual. Following the record strong El Niño of 1997-98, La Niña almost immediately set in the following summer, reaching moderate-to-strong intensity before finally ending in spring 2001.
A similar situation occurred following the strong El Niño of 1972-73. However, neutral conditions followed three other strong El Niños of 1982-83, 1965-66 and 1957-58.

What Does It Mean for Your Forecast?

Summer 2016

There are some broad trends that have shown up in past weakening El Niño events that could give a hint on what to expect this summer.
(MORE: Summer Outlook 2016)
"If we look at rapidly decaying historical ENSO events (trends, instead of actual values), we see that the summer heat is centered in the northern Plains into the Great Lakes states," said Dr. Todd Crawford, chief meteorologist at The Weather Company's energy division.

A summer 2016 temperature outlook, issued in May 2016, by The Weather Company, an IBM Business.

Atlantic Hurricane Season 2016

Strengthening El Niños during the Atlantic hurricane season tend to yield stronger wind shear, which tends to tear apart developing or mature tropical cyclones.
Sure enough, June through Oct. 2015 Caribbean wind shear was the highest on record dating to 1979, according to Dr. Phil Klotzbach, tropical scientist at Colorado State University.

Klotzbach also found that the chance of a U.S. hurricane impact rises dramatically in a La Niña or neutral (neither El Niño or La Niña) season compared to an El Niño season.

This at least loads the dice a bit toward an increased chance of tropical cyclones surviving into the Caribbean Sea, or forming there, particularly later in the season as El Niño disappears farther in the rear-view mirror.
If El Niño was the only factor, that is.
The odds may shift a bit toward a more active Atlantic hurricane season in 2016, but El Niño's absence doesn't guarantee that outcome.
As we wrote in Jan. 2016, prior hurricane seasons after strong El Niños have produced anywhere from only four named storms (1983) to 14 named storms (1998), three hurricanes (1983) to 10 hurricanes (1998).
This fizzled El Niño also doesn't mean the season poses any greater threat to the U.S. compared to any other year, as landfalls tend to be poorly correlated with numbers of named storms.
(MORE: 2016 Atlantic Hurricane Season Outlook)

Winter 2016-17

We've said many times an El Niño, La Niña, or the lack of either, known as the neutral phase, is only one large-scale forcing on the atmosphere. It is not the be-all and end-all determining whether a season is wet, dry, cold or warm.
Despite that, the peak atmospheric response to the equatorial Pacific anomalies tends to occur in the northern hemisphere winter months.
So, in the event we have a La Niña settling in by fall or winter, let's take a look at December-February U.S. temperature and precipitation anomalies during weak (SST anomalies from 0.5 to 0.9 degrees below average), moderate (1.0 to 1.4 degrees below average) and strong (1.5 degrees below average or cooler) La Niñas.
Temperatures
While there are some differences among La Niña magnitudes, some commonalities emerge regarding La Niña winter forcing in the U.S.:

• Cold: Northern Plains, Upper Midwest, New England, New York state, West Coast
• Warm: Southern Plains, Southeast

Neglecting other factors, it appears the stronger the La Niña, the stronger the likelihood the winter warmth spreads farther north into the Corn Belt, Ohio Valley and mid-Atlantic states.

December-February temperature anomalies (degrees Fahrenheit) during 11 weak, 6 moderate, and 3 strong La Niña events dating to 1950, using the classification scheme from Jan Null.

Precipitation
Again, despite some differences among La Niña magnitudes, some commonalities are apparent:

• Wet: Pacific Northwest, Bitterroots (western Montana/Idaho), parts of the Ohio Valley, Tennessee Valley
• Dry: Southern Plains, Gulf/Southeast coast including Florida, Southern California, Desert Southwest

December-February precipitation anomalies (inches) during 11 weak, 6 moderate, and 3 strong La Niña events dating to 1950, using the classification scheme from Jan Null.

MORE: NASA Climate Change Satellite Images