Posted by Elisabeth Gawthrop on December 23, 2015
Read our ENSO Essentials & Impacts pages for more about El Niño.
Tony Barnston provides an overview of the briefing
As of mid-December, sea-surface temperatures across the equatorial Pacific were stable or down slightly compared to late November (see first image in first gallery). Tony Barnston, IRI’s chief climate forecaster, said the peak strength with respect to this metric of the El Niño event may have passed. There is still a chance for another resurgence, he said, but not if current trends continue.
Regardless of the timing of the strongest sea surface temperatures, many areas will still see impacts of El Niño for the next several months.
Given the current strength of the event, slight weakening is not likely to significantly diminish the atmospheric processes that influence climate around the world.
Convection (i.e. rain storms) along the equator in the central Pacific is the major contributor to these processes and has been increasing since early November after a brief lull (see second image in first gallery).
Because El Nino’s effects differ by season and region, its impacts may be winding down in some areas, such as its influence on the rainy season in eastern equatorial Africa. Others are just beginning, including the signal of a wet winter in the southern U.S., the mid-Atlantic coast and California (see seasonal forecasts below).
The probability that El Niño will continue, at least at a weak level, remains around 100% through the first few months of 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.
Changes from last month’s briefing
Sea-surface temperatures in the region that defines El Niño, called Nino3.4, have very slightly declined over the last month.
Barston said, however, that we are clearly still in a broad, long-lasting peak spanning from mid-October to likely mid-January.
“The recurrence of a burst of more strongly-weakened trade winds in the western or central tropical Pacific could lead to a secondary peak in sea surface temperature, but there is no guarantee that this will happen,” he said.
Last week, sea surface temperatures (SSTs) in the Nino3.4 region (see first image in second gallery) were 2.9ºC above average. The SST anomaly for the month of November was +2.96ºC (October was 2.46ºC, September was 2.28ºC). [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.]
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 begin 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.
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 January-March period, the forecast shows a strong likelihood of drier-than-normal conditions over areas of northern South America, southern Africa, western Australia, Indonesia, the Philippines and parts of the northern US and southern Canada (image above).
There are also increased odds for drier-than-normal conditions in western Alaska, western Africa, Sri Lanka and central southwest Asia.
The southern US, northern Mexico and the northern Caribbean have a high chance of above-average rainfall, and exceptionally so over Florida and surrounding areas. Southeastern South America, eastern China and parts of the Peru/Ecuador coast 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 January-March 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.