January Climate Briefing: Strong El Niño Will Persist

Read our ENSO Essentials & Impacts pages for more about El Niño.

Tony Barnston provides an overview of the briefing

El Niño’s peak in tropical Pacific sea surface temperature came in late 2015, but the event is expected to stay strong, with climate impacts likely for the first few months of 2016. Recent wind patterns could lead to more Kelvin wave activity, which could in turn make the El Niño linger even into May. 

While scientists use sea surface temperature to officially define El Niño, convection (i.e. rain storms) along the equator in the central Pacific is thought to be the major contributor to setting in motion the atmospheric processes that influence climate around the world. Convection has been steady near and to the east of the international date line (see bottom center of first figure), but it has not stretched as far to the east as during the 1997-98 El Niño, according to Anthony Barnston, IRI’s Chief Forecaster. 

Will the above average convection continue? Yes, but not indefinitely. Tropical Pacific sea-surface temperatures must stay high for the convection to continue, but due to the oscillating nature of El Niño, the sea surface temperatures will almost certainly return to average as the year progresses. The SSTs will cool more slowly, however, if the winds along the equator remain conducive to maintaining the above-average ocean temperatures. The current strong westerly wind burst is triggering a Kelvin wave that will move eastward toward South America, raising ocean temperatures, or at least preventing them from cooling as quickly, both below and at the ocean surface. The resulting maintenance of well above-average sea-surface temperatures will in turn maintain the above-average convection along the equator, which will keep the climate impacts of El Niño in force around the globe.  In the second image of the gallery below, the yellows and reds indicate areas where the trade winds have reversed direction and are instead blowing to the east. At the bottom is the most recent burst of such winds.

Outgoing longwave radiation is displayed, with blue tones indicating more convection, and orange tones indicating less convection. Time increases down the vertical axis. The horizontal axis represents longitude, and data is averaged from 5ºS to 5ºN along the equator.

Zonal winds, or winds that blow in the east-west direction, along the equator are displayed, with positive numbers indicating winds from the east and negative numbers indicating winds from the west. Time increases down the vertical axis. The horizontal axis represents longitude, and data is averaged from 2ºS to 2ºN along the equator.

El Niño’s effects differ by season and region, so its influence in some areas is winding down, while other areas are just starting to see impacts. See this map for typical El Niño impacts by season and region, and see our seasonal forecasts below for the latest on the upcoming seasons.

According to model predictions, the probability that El Niño will continue, at least at a weak level, remains around 100% through the March-May season. The probability of El Niño then drops off quickly, with odds of neutral conditions eclipsing those of El Niño by the May-July season. 

Changes from last month’s briefing

Last week, sea-surface temperatures in the Nino3.4 region (see first image in second gallery) were 2.6ºC above average. The SST anomaly for the month of December was +2.82ºC (November was 2.95ºC, October was 2.46ºC). The highest weekly Nino3.4 SST value recorded was 3.1ºC in mid-November. [Note: For many reasons outlined in this NOAA blog post, comparison of SSTs between datasets (and sometimes even within the same dataset!) should be cautious, largely due to variation in data collection methods and resolution of the datasets. Further, the dataset used for the above statistics (called OISSTv2) is not the one used in NOAA’s records for official peak strength (called ERSSTv4), though OISSTv2 is the one used in initializing models.] 

The sea surface temperatures in the Nino3.4 region (approximated here) serve as a primary metric of El Niño conditions.

This graph shows forecasts made by dynamical and statistical models for SST in the Nino 3.4 region for nine overlapping 3-month periods. Note that the expected skills of the models, based on historical performance, are not equal to one another.

The IRI/CPC probabilistic ENSO forecast issued mid-January 2016. Note that bars indicate likelihood of El Niño occurring, not its potential strength. Unlike the official ENSO forecast issued at the beginning of each month, IRI and CPC issue this updated forecast based solely on model outputs. The official forecast, available at http://1.usa.gov/1j9gA8b, also incorporates human judgement.

To predict El Niño, computers model the SSTs in the Nino3.4 region over the next several months. The graph in the second image of the second gallery shows the outputs of these models, some of which use equations based on our physical understanding of the system (called dynamical models), and some of which used statistics, based on the long record of historical observations.

The means of both the dynamical and statistical models call for the El Niño event to continue to weaken, and they are largely in agreement for the next four or so months. They project the event will stay at or above the +1.5ºC “strong” El Niño threshold through the February-April season, and above the +0.5ºC “weak” El Niño threshold through the April-June season. Looking past June, the dynamical models call for a swing into weak La Niña conditions, while the statistical models favor a neutral Northern Hemisphere late summer and early autumn. The model’s ability to predict past June, however, tends to be weak, so long-range forecasts carry higher uncertainty. This uncertainty is apparent in the large spread of the model’s predictions past the May-July season. 

The El Niño advisory issued in March by the National Oceanic and Atmospheric Administration’s Climate Prediction Center and IRI is still in effect.

Effects of El Niño on global seasonal forecasts

Each month, IRI issues seasonal climate forecasts for the entire globe. These forecasts take into account the latest ENSO SST projections and indicate which areas are more likely to see above- or below-normal temperatures and rainfall.

Just as last month, the probabilities for wetter- or drier-than-usual conditions are some of the strongest ever seen.

For the upcoming February-April period, the forecast shows a strong likelihood of drier-than-normal conditions over areas of northern South America, southern Africa, central Africa, southeast Asia and western Canada (image above). There are also increased odds for drier-than-normal conditions in western Alaska, the northern US, western Africa, southern India and Sri Lanka. The southern US, northern Caribbean and coastal Ecuador and Peru have a high chance of above-average rainfall. Southern Brazil and eastern Paraguay also have increased chances of above-average precipitation.

El Niño in context: Resource page on climate variability

The impacts listed above are specifically for the February-April season. Some of these impacts are predicted to persist in the following seasons, but some areas see different impacts in the other seasonal windows. See forecast maps in the image gallery and on our seasonal forecast page.

Learn more about El Niño on our ENSO resources page, and sign up here to get notified when the next forecast is issued. In the meantime, check out #IRIforecast or use #ENSOQandA on Twitter to ask your El Niño questions.