November Climate Briefing: El Niño Takes the Wheel
Read our ENSO Essentials & Impacts pages for more about El Niño.
Tony Barnston provides an overview of the briefing
Is it 1997?
Rapid strengthening of the ongoing El Niño event over the last several weeks has made headlines, some saying that its strength has eclipsed that of the 1997-98 “super” El Niño event. But Tony Barnston, IRI’s chief climate forecaster, cautions that while this event is strong, the weekly average of the sea surface temperatures cited as evidence for this El Niño’s strength is not what will be primarily used to judge its official peak strength. Monthly and three-month averages are a better gauge of strength because El Niño influences global climate more reliably on these timescales. More on the importance (or lack thereof) of weekly data is available on this NOAA ENSO blog post.
If the recent uptick in weakly average sea surface temperatures (SSTs) persists, however, the event could surpass the 1997-98 El Niño. “But persistence of such high SSTs for three months, or even one month, is by no means guaranteed,” said Barnston.
Not all El Niños are created equally
Barnston also stressed that there are other differences from 97-98, including the location of the strongest SSTs and the differences in SST patterns in other parts of the Pacific and Indian Oceans. This could cause impacts in some areas to deviate somewhat from those seen in 97-98. “For example, while the entire tropical Indian Ocean SSTs are well above average, the SSTs in the western Indian Ocean are not much more above average than those in the eastern Indian Ocean,” said Barnston. This SST pattern is different from that in 1997-98, when this relative index of SSTs between the western and eastern Indian Ocean, known as the Indian Ocean Dipole, was more positive. “This could somewhat weaken the expected above-average rainfall in eastern equatorial Africa during the final months of 2015,” said Barnston.
Another area influenced by varying SST patterns is the northwestern coast of South America. Countries such as Peru and Ecuador are more likely to experience heavy rainfall if the SSTs close to them are much above average. At the time of this writing, SSTs along the coast are higher than normal, but not the extent they were in 1997-98 at this time of year, or to the those seen currently in the central Pacific.
Models project the event will start to weaken in early 2016, but they indicate it will stay above the +1.5ºC “strong” El Niño threshold for the February-April season. 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.
Regardless of whether this El Niño statistically falls short of the 97-98 event, it will be a very strong event. Impacts are expected globally, especially in the tropics, and have already begun in some areas (see seasonal forecasts below).
Changes from last month’s briefing
Sea-surface temperatures in the region that defines El Niño, called Nino3.4, have continued to warm over the last month. Last week, sea surface temperatures (SSTs) in the Nino3.4 region were 3.0ºC above average (see image, top left), a record for this region on the weekly timescale since the dataset began in 1990. The SST anomaly for the month of October was +2.46ºC (September was 2.28ºC, August was 2.07ºC). [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 is not the one used in NOAA’s records for official peak strength, though it 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 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 the dynamical models calls for an event peaking between just above 2.5ºC in the November-January season. The statistical models project a peak just below the 2.5ºC mark, but well above the +1.5ºC “strong” El Niño threshold. For the past several months, observations have been tracking on the high end of what statistical models have predicted, and more or less in the middle of the cluster of what the dynamical models have predicted.
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 December-February period, the forecast shows a strong likelihood of drier-than-normal conditions over broad areas of northern South America, southern Africa, western Australia, 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, western Africa and western Alaska. The southern US and northern Caribbean have a high chance of above-average rainfall, and exceptionally so over Florida and surrounding areas. Southeastern South America and eastern China 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 December-February 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.
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