El Niño is expected to weaken but slowly

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  • Average SSTs for the Pacific in the last moth. Credit of the Picture: NASA.

    Upper-Oceand Heat anomalies from March 2016 to February 2016. Credit of the picture: NASA.

    Most models predict a continuing weakening of El NIño. Credit of the picture: NASA.

    CFSvS model, predicting a long-lasting El Niño. Credit of the picture: NASA

  • El Niño is expected to weaken but slowly
    27.02.2016 16:51

    2015 recorded one the strongest El Niños. From November it has been slowly weakening with a transition expected to neutral conditions by next summer, although some models predict El Niño to last for much of 2016. Let’s summarise the main facts.

    By historical standards to be classified as a complete El Niño episode, the Oceanic Niño Index (ONI) needs to have a positive ONI greater or equal to +0.5C in the Sea Surface Temperature (SST) for a period of at least 5 consecutive months. 2015 saw a significant increase in SSTs across the eastern Pacific from January to March, staying well above from August to September and finally reaching the highest SST around +2.0C in November. Since then, SSTs started to fall but January saw a rise in SSTs for a time, although it fell again during February.

    For mid-February this year, there is still a greater extent and magnitude of high SST anomalies in depth over the Central and Eastern Pacific than in late winter after the previous 2 El Niños. Also, the location of the peak SST anomalies over the Tropical Pacific is further west than the other 2 El Niños, both of which faded from the west.

    In Feb 1983 and 1988, there was a shallower layer of warm water over the surface and near surface waters of the Tropical Pacific and a larger and more substantial body of cold sub-surface water that shifted eastwards and upwards towards the surface during the spring of these years. This body of cold sub-surface water is less developed this year so far.

    2016 peaked at a similar time to the 1997-98 El Niño, while 1982-83, peaked in Jan 1983. La Niña conditions followed 8/12 of the best El Niño surface analogues compared to the 2015-16 event, with the strongest 3 El Niños (1997-98, 1982-83 and 1973-74) all going into La Niña by the following autumn/winter. However, the 2015-16 El Niño is something of a special case, with much warmer sub-surface water over the tropical Pacific than the 8 best analogues. This suggests that there is a risk that the transition from El Niño to ENSO neutral conditions this spring and early summer may be somewhat slower than previous examples, unless this deeper sub-surface water can be quickly displaced by strong sub-surface cooling from the west over next month or so. However, some models hint that El Niño may remain throughout the year

    So far, El Niño related-events have caused an above normal tropical cyclones season in the Pacific with the strongest storm to make landfall called Winston that ravaged the Fiji Islands. Pali typhoon was the earliest hurricane formed this January and three simultaneous hurricanes called Kilo, Jimena and Ignacio developed last August. In contrast, the Atlantic season was mainly quiet with no significant storms. El Niño is likely related to the warmest year globally on record in 2015 and the so-called “Snowzilla” that hit the east coast of the USA with very large snowfalls. Other extreme events are likely to be waiting in store. Therefore, you should keep posted by looking at our website, apps or social networks.

    By: Mario Cuellar