October Climate Briefing: El Niño Flexes Its Strength

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

Tony Barnston provides an overview of the briefing

Changes from last month’s briefing

The El Niño that officially began last March and became a “strong” event in July continues to strengthen, with the event expected to peak in the next few months. Even with the weakening projected by models in early 2016, most models show an event still above the +1.5ºC “strong” El Niño threshold for the January-March season. The probability that El Niño will continue, at least at a weak level, remains around 100% through early 2016 — in line with what has been forecasted by IRI and the National Oceanic and Atmospheric Administration’s Climate Prediction Center the last several months.

Barnston says recent westerly wind anomalies in the western Pacific, and the Kelvin waves associated with them, continue to strengthen the El Niño and make it competitive to reach the strength of the 1982-83 and 1997-98 events, which are the strongest two events since 1950. While it may still fall short of the 97-98 event, it will be a very strong event nonetheless. Impacts are expected globally, especially in the tropics, and have already begun in some areas (see seasonal forecasts below).

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-October 2015. 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.

Sea-surface temperatures in the region that defines El Niño, called Nino3.4 (see image), have continued to warm over the last month. Last week, sea surface temperatures (SSTs) in the Nino3.4 region were 2.4ºC above average (see image, top left). The SST anomaly for the month of September was +2.28ºC (August was 2.07ºC, July was 1.6ºC).

To predict El Niño, computers model the SSTs in the Nino3.4 region over the next several months. The graph in the top right image 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 mean of both statistical and dynamical models call for an event peaking between 2.0ºC and 2.5ºC in November-January season, well above the +1.5ºC “strong” El Niño threshold. For the past several months, observations have been tracking on the high end of what models predicted. In fact, observed sea surface temperatures eclipsed nearly all of the statistical models’ predictions during the northern hemisphere’s summer months.  The dynamical models were closer to observations over the summer. Last year, however, the statistical models proved to be a little more accurate. See images below, and full details on our current forecast page.

This plot shows the model forecasts issued in the current month as well as from the 21 months previous to this month. The observations are also shown up to the most recently completed 3-month period. The plots allow comparison of plumes from the previous start times, or examination of the forecast behavior of a given model over time. This plot shows forecasts for statistical models. For less difficult readability, forecasts are shown to a maximum of only the first five lead times.

This plot shows the model forecasts issued in the current month as well as from the 21 months previous to this month. The observations are also shown up to the most recently completed 3-month period. The plots allow comparison of plumes from the previous start times, or examination of the forecast behavior of a given model over time. This plot shows forecasts for dynamical models. For less difficult readability, forecasts are shown to a maximum of only the first five lead times.

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 November-January period, the forecast shows a strong likelihood of drier-than-normal conditions over broad areas of northern South America, the Caribbean, Indonesia and the Philippines (image above). There are also increased odds for drier-than-normal conditions in parts of the northern US and southern Canada, southern Africa, central South America, Australia and New Zealand. Some of these regions are adjacent to areas very likely to have wetter-than-average conditions, such as southern South America and eastern-equatorial Africa. Ecuador, the southern US, central India and far-western and far-eastern Asia 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 November-January 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.

Forecast in Brief

Download a PDF summary of the October IRI Climate Briefing