March Climate Briefing: El Niño Impacts Still Likely

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

Tony Barnston provides an overview of the briefing

Due to sustained above-average sea surface temperatures in the Nino3.4 region of the central equatorial Pacific Ocean (see first image in gallery), the ongoing El Niño event continues to remain in the strong category.  While the event is expected to quickly weaken in the next few months, cloudiness and thunderstorms — described as convection — continue to be above average in the equatorial Pacific (see second image). This convection, shown in blue in the image, is what scientists believe triggers the changes in atmospheric patterns around the globe. In the last weeks, the area of convection has expanded somewhat eastward.

Convection activity tends to quickly follow above-average sea surface temperatures, but the effects of the convection on global climate patterns lag by several weeks. So, as this convection continues, climate impacts in some regions are expected for the upcoming season (see forecasts near end of post). 

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

Outgoing longwave radiation is displayed, with blue tones indicating more convection, and orange tones indicating less convection. Time increases down the left axis. The bottom axis represents longitude, and data is averaged from 5ºS to 5ºN along the equator. Source: Climate Prediction Center/NCEP

Changes from last month’s briefing

Last week, sea-surface temperatures in the Nino3.4 region (see first image) were 1.7ºC above average. This figure is just above the +1.5ºC threshold indicating a “strong” El Niño. The SST anomaly for the month of February was +2.40ºC (January was +2.60ºC, December was 2.82ºC). 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.] 

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-March 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 first 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 use statistics, based on the long record of historical observations.

While the means of the models show a similar output to that of last month’s forecast, the spread of the models has increased since last month, indicating some uncertainty in the predictions for later in the year. The means of both the dynamical and statistical models call for the El Niño event to continue to weaken. They project the event will stay above the +0.5ºC “weak” El Niño threshold through the April-June season. Looking to the Northern Hemisphere autumn, both dynamical and statistical models are approaching a borderline La Niña state (-0.5ºC) by the August-October season.

Though models’ ability to predict past June tends to be weak, there is more certainty coming out of a strong El Niño year due to scientists’ understanding of the physical processes of El Niño Southern Oscillation. Nonetheless, long-range forecasts carry higher uncertainty than short-term. El Niño conditions are unlikely for the latter half of 2016, but it’s not possible to determine yet whether neutral or La Niña conditions will prevail. 

According to model predictions, the probability that El Niño will continue, at least at a weak level, remains near 100% through the current March-May season. The probability of El Niño then drops off quickly. Just as in last month’s forecast, odds of neutral conditions (65%) are more than double those of El Niño conditions (just over 30%) for the May-July season. For the final season in the forecast, November-January, the odds of La Niña conditions just top 50%.

The El Niño advisory issued in March 2015 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 sea surface temperature projections and indicate which areas are more likely to see above- or below-normal temperatures and rainfall.

For the upcoming April-June period, the forecast shows a strong likelihood of drier-than-normal conditions over areas of northern South America, southeast Asia and parts of far eastern Russia (first image in gallery above, click to enlarge). Parts of southeastern South America as well as coastal Ecuador show high chances of above-average precipitation. Central southwest Asia as well as Alaska and the southern US show a slightly elevated chance of above-average precipitation. 

El Niño in context: Resource page on climate variability

The impacts listed above are specifically for the April-June season. By the June-August season, the ENSO-neutral conditions expected in the Pacific Ocean lend little signal for seasonal forecast prediction. 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.