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WMO El Niño/La Niña Update

19 October 2016

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Current Situation and Outlook 

Since July 2016, tropical Pacific Ocean surface temperatures have approached or marginally exceeded weak La Niña levels. However, a clear atmospheric component of the El Niño/Southern Oscillation (ENSO) pattern has not become evident until recent weeks. Since early October trade winds have strengthened over the tropical Pacific Ocean, indicating that a La Niña-like atmospheric circulation pattern may be developing.

Around half of the climate models surveyed predict that weak La Niña conditions will develop during the last quarter of 2016, while the remaining models suggest a weakening to more clearly defined ENSO-neutral conditions. On the whole, model outlooks and expert opinion indicate that there is a 50-60% probability of weak La Niña conditions forming in the last quarter of 2016, and persisting into the first quarter of 2017. National Meteorological and Hydrological Services will continue to closely monitor changes in the state of ENSO over the coming months.

Following near-average ocean temperatures in the central and eastern tropical Pacific Ocean during May and June 2016, temperatures cooled to about 0.5 degrees Celsius below average by early July and have remained close to that level through early October. This slightly below-average ocean temperature is near the threshold of weak La Niña.

However, until late September the atmospheric indicators were mixed, with some suggesting weak La Niña and others indicating neutral conditions. Most notably, low-level trade winds had not been consistently stronger than average over substantial portions of the tropical Pacific as would be expected during La Niña. However, as a result of an active phase of the Madden Julian Oscillation, a tropical disturbance of clouds, rainfall, winds, and pressure that propagates eastward around the global tropics, recent weeks have seen somewhat stronger than average trade winds re-emerge in the central-west tropical Pacific Ocean.

The recently enhanced trade wind strength increases the potential for enhanced ocean-atmosphere coupling that could maintain, or further strengthen La Niña patterns. Hence if the recently strengthened trade winds persist and extend farther east in the tropical Pacific basin, there is a far greater chance for the strengthening of the coupling needed for La Niña to more clearly develop and continue into early 2017.

Around one half of the dynamical and statistical prediction models surveyed predict 3-month average sea surface temperatures in the east-central tropical Pacific Ocean to remain at least one-half degree Celsius below average during the fourth quarter of 2016, with some models predicting further cooling to near 1.0 degree Celsius below average. However, other models predict the temperatures to slowly return towards average between now and early 2017. This variation among the predictions reflects some model differences in the degree of predicted participation of the atmosphere, and the extent and time duration over which the temperature of the water below the surface will remain below average. Current estimations of probabilities for La Niña conditions in late 2016 range from 35 to 75%, with an average near 50-60%. Models indicate virtually no chance of development of El Niño during 2016 or the earliest months of 2017.

A careful watch will be maintained on the oceanic and atmospheric conditions in the tropical Pacific Ocean in the coming months to assess the possible transition to La Niña.

It is important to note that El Niño and La Niña are not the only factors that drive global climate patterns. Further, the strength of a La Niña event may not necessarily closely correspond to its climate impacts occurring in various regions of the world. At the regional level, seasonal outlooks need to assess the relative impacts of El Niño/La Niña state and other locally relevant climate drivers. For example, the sea surface temperature of the Indian Ocean, the southeastern Pacific Ocean and the Tropical Atlantic Ocean are also known to influence the climate in the adjacent land areas. Regionally and locally applicable information is available via regional and national seasonal climate outlooks, such as those produced by WMO Regional Climate Centres (RCCs), Regional Climate Outlook Forums (RCOFs) and National Meteorological and Hydrological Services (NMHSs).

In summary:

  • The tropical Pacific Ocean has slowly cooled to La Niña thresholds during September and October. However, it is only in recent weeks that a La Niña-like pattern in the atmosphere has become evident.
  • Models surveyed and expert opinion suggest that La Niña is approximately 50-60% likely during the last quarter of 2016, persisting into early 2017.
  • The most likely strength of La Niña, if it prevails, is weak; however, further strengthening to moderate levels cannot be ruled out.
  • There is virtually no chance of El Niño re-development in 2016 or early 2017.
The state of ENSO will be carefully monitored. More detailed interpretations of regional climate variability will be generated routinely by the climate forecasting community over the coming months and will be made available through the National Meteorological and Hydrological Services. For web links of the National Meteorological Hydrological Services, please visit:

http://www.wmo.int/pages/members/members_en.html

For information on WMO Regional Climate Centres (RCCs) and links please visit:

http://www.wmo.int/pages/prog/wcp/wcasp/RCCs.html





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