Strongest El Niño in Decades

El Niño/Southern Oscillation (ENSO)

Seasonal forecasting is a developing science. Skill is required for the scientific production of the forecast, but also in interpreting the information. However, if there is ever going to be a good time to check these long range forecasts, it is now.

Enhanced Predictability

The latest seasonal forecasts (months to seasons ahead) are currently showing an enhanced level of confidence, with many of the forecasting centres around the world in good agreement. Confidence in seasonal forecasting is based on climatic rhythms and patterns that stretch across the globe with regional impacts.

So, why are seasonal forecasters more confident right now? It’s all down to the most studied and well-understood mode of climate variability, the El Niño-Southern Oscillation (ENSO). We are in a strong positive phase (“warm phase” or El Niño) which may still get stronger.


Source: NOAA CPC

It is expected to be one of the strongest El Niño phases in the last half-century, and the most intense since 1997-1998, according to a recent World Meteorological Organisation report.

Seasonal forecasting, especially around the tropics, relies heavily on ENSO so confidence in long-range predictability is currently as high as it can be.

The indicators for the phases of ENSO (El Niño or its “cool phase” sister La Niña) include fluctuations in sea surface temperatures in the equatorial Pacific, coupled with changes in the air pressure differential between the tropical eastern and western Pacific regions. When these factors align, a globally linked set of impacts increase their chances of occurring, associated with the development of either an El Niño or La Niña.


Quick facts on ENSO phases:

  • Tend to start developing during April through June.
  • Normally persist for around a year, sometimes two.
  • Recur every 2 to 7 years.

An El Niño is not an individual storm or single period of drought, instead it’s a combination of multiple events happening within the same time frame around the world.

The last time an El Niño was this strong was in 1997-1998. The impacts were severe and widespread, including record-breaking rainfall and flooding in California, leading to damage estimates around at least $550 million and severe tornado outbreaks in Florida and other southern states. Droughts also ravaged Indonesia and Australia. With such an influx of heat into the atmosphere at the beginning of the year, 1998 also became the hottest year on record globally (at that time).

However, every El Niño is different, so this one will be watched closely for any new patterns that emerge due to global changes since the late 1990’s—especially in factors like sea ice and snow cover. Already, 2015 is on track to become the new warmest year on record.

A Word of Caution

Confidence in the forecast isn’t always so high – last year was different.  ENSO forecasts back in early 2014 were suggesting an enhanced chance for a weak to moderate El Niño to develop, with some computer models indicating it may even become a strong one. It failed to materialise in 2014, leading to what many perceived as a forecast ‘bust’. It took until the end of 2014 before a much stronger signal began to emerge in the models, which led to our current El Niño conditions.

Even as far back as November 2014, the International Research Institute for Climate and Society (IRI) forecasts were calling for a weak to moderate El Niño to develop, and through last winter, the indications strengthened and we have now ended up with the strongest El Niño in decades.

Latest Long-Range Forecasts

Our Willis Research Network partners at the National Center for Atmospheric Research produce summaries of the latest thinking in long-range atmospheric forecasting from around the world, primarily focused on the main insurance markets. Our latest seasonal forecast summary is available here.

Many of the signals are typical of a strong El Niño, and expressed as shifts in probabilities of seasonal parameters such as temperature, precipitation and storminess. Shifts away from normal for many areas broadly include:

  • U.S.: Increased odds of wet and cool conditions over Southern States, and drier than normal conditions over the Pacific Northwest and the far Northeast.
  • Australia: Increased odds of warmer than normal temperatures for southern regions. Increased odds of drier than normal conditions for the southeast and northeast.
  • Europe: Increased odds of wetter and stormier than normal conditions.
  • Indonesia: Strong signal for drier than normal conditions.

A ‘Go-to guide’ is also available here to provide a more detailed background on the science behind seasonal forecasts. If this information can be used and developed to guide pricing and capital allocation decisions, we may be able to improve the way we build in better risk management decisions via the insurance industry.

About Geoffrey Saville

Geoffrey Saville is a member of Willis Towers Watson's Analytics Technology Team, having joined the company in 2013…
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