March Climate Briefing: Probability of El Niño Rises

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

Since last month’s briefing, weekly sea-surface temperature anomalies have ranged from -0.2ºC to +0.3ºC in the area of the central equatorial Pacific Ocean that define El Niño and La Niña events, called the Nino3.4 region. This is firmly in the range of neutral ENSO conditions, although other indicators of ENSO present some conflicting signals. The first image below shows the latest week’s anomalies.

While the sea-surface temperatures (SSTs) point to a neutral ENSO state, the convection patterns in the equatorial Pacific (i.e. at what longitudes along the equator clouds and thunderstorms form) continue to show a La Niña-like pattern in the central and western part of the tropical Pacific basin (see second image in below gallery). This pattern is lingering longer than scientists expected — it’s persisting despite the warming sea surface temperatures in the area.

Adding to the unusual nature of the current ENSO state is the warming seen in the eastern Pacific Ocean along the coast of South America. Sea-surface temperature anomalies in this area, referred to by scientists as the Nino1+2 region, have been approaching +2.5ºC in the last couple of weeks (see third image in below gallery). While these warm temperatures can have significant climate impacts locally, they do not carry much influence on global climate.

The National Oceanic and Atmospheric Administration’s Climate Prediction Center’s ENSO alert system status is currently listed as Not Active.

The sea-surface temperatures in the Nino3.4 region (approximated here) serve as a primary metric of El Niño and La Niña conditions. Data from the IRI Data Library. Image: IRI/Elisabeth Gawthrop

ENSO Forecasts

To predict ENSO conditions, computers model the SSTs in the Nino3.4 region over the next several months. The graph in the first image of the gallery below 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 use statistics, based on the long record of historical observations.

The means of both the dynamical and statistical models have increased since last month, with both calling for SSTs above the El Niño threshold of +0.5ºC later in the year. The statistical model mean only just exceeds the threshold, staying in the range of a weak El Niño event. The dynamical model mean reaches +1.0ºC, which translates to a moderate El Niño event. 

These forecasts, however, extend past what’s known as the spring predictability barrier — a function of ocean dynamics that makes it hard to predict ENSO past June of each year, so uncertainty is high and an El Niño event is not guaranteed.

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.

Based on these model outputs, odds for La Niña are close to zero for the next several seasons, with neutral conditions most likely during the first two seasons (see second graph in gallery above). The warmer SSTs shown in the plume graph, especially in the dynamical models, are reflected in the increasing likelihood for El Niño conditions later in the year. The odds of El Niño conditions are highest during the northern hemisphere summer, approaching 70%.

ENSO in context: Resource page on climate variability

The official probabilistic forecast issued by CPC and IRI in early March shows a similar overall pattern, but with odds for El Niño conditions slightly lower, topping out between 50-55%. This early-March forecast uses human judgement in addition to model output, while the mid-March forecast relies solely on model output.

While a back-to-back El Niño-La Niña-El Niño sequence is not typical, it’s not unprecedented. According to Barnston, it’s happened once since 1950 — in 1963, 1964 and 1965.

Effects of La Niña on global seasonal forecasts

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

For the upcoming seasons, the forecast shows little signal from ENSO, as would be expected given the neutral ENSO forecast. The exception is Indonesia, where there is a slightly increased chance for below-average precipitation in the northern hemisphere summer months. The forecast maps are available on our seasonal forecast page.

Learn more about El Niño and La Niña on our ENSO resources page, and sign up here to get notified when the next forecast is issued. In the meantime, check out #IRIforecast.