Updated on 24 January 2017

In November 2016, the cool anomalies of the equatorial Pacific Ocean’s sea-surface temperature (SST) Niño3.4 region weakened further and the value remained neutral for that month (Figure A). Atmospheric variables, such as trade winds and cloudiness, over the equatorial Pacific showed either weakening La Niña or neutral conditions. The Niño3.4 index for December 2016 was -0.31 (Figure B). The latest 3-month average (October-December) is -0.46, which is within the neutral threshold. The Niño3.4 index above is based on non-detrended SST data that includes a long-term trend over the ocean due to on-going global warming. This partly reduces the magnitude of the SST cold anomalies during a La Niña episode (while increasing the anomalies during an El Niño episode).  In that respect, the presence of large scale wetter-than-normal rainfall conditions for the region in December 2016 (Figure C) are consistent with rainfall anomaly patterns during La Niña events.

Climate models favour neutral conditions from the December-February (DJF) 2016-17 season onwards (Figure D) and remaining cool SST anomalies over the Niño3.4 region are predicted to fade by April 2017 (Figure E).

Impact of El Niño/La Niña on Southeast Asia

Typically the impact from La Niña for Southeast Asia is wetter-than-normal rainfall conditions except over much of Borneo and Southern Sumatra during November to January (Figure F). During El Niño events the opposite, i.e. drier-than-normal conditions, normally occurs. Locally-specific impact differs from place to place and for different seasons.

No two El Niño events or two La Niña events are alike in terms of their impact on the region’s rainfall and temperature. Furthermore, the strength of events and the corresponding impact do not always scale. For example, there were years where relatively weaker El Niño/La Niña events induced more significant changes in rainfall than the stronger events.

    Figure A: Warm shades show regions of relative warming, while cool shades show regions of relative cooling with respect to 1971-2000 climatology for December. On average, the tropical Pacific Ocean Niño3.4 region (red box, 120°W-170°W and 5°S-5°N) was still slightly cooler than normal but had weakened to neutral from November 2016 (image credit: IRI Map Room).

 

    Figure B: Monthly sea-surface temperature (SST) anomaly over the Niño3.4 region (120°W-170°W and 5°S-5°N) of the tropical Pacific Ocean from Jan 2016 to Dec 2016 (image credit: IRI Map Room). Both SST and atmospheric responses over the tropical Pacific Ocean indicate either weakening La Niña or neutral conditions.

 

    Figure C: Spatial rainfall anomaly patterns in the region for December 2016 showing large scale, wetter-than-normal conditions for the region (image credit: IRI Map Room). Brown (green) shades show drier (wetter) than the average climatological rainfall for October (1970 – 2009). Quantitative anomaly values are only indicative due to limitations in the data source.

 

    Figure D: Probability of El Niño (red), La Niña (blue) and neutral conditions (green) for late 2016 and much of 2017. Neutral conditions are favoured from Dec-Feb 2016-2017 season onwards (image credit: IRI-CPC).

 

    Figure E: Forecasts of Niño3.4 index’s strength for the late 2016 and much of 2017 from various seasonal prediction models of international climate centres. Values above 0.5°C indicate El Niño conditions, below -0.5°C indicate La Niña conditions, and in between indicate neutral conditions, i.e. neither El Niño nor La Niña. Models predict the cool anomalies to weaken further (image credit: IRI-CPC).

 

    Figure F: November to January rainfall anomaly composite for La Niña years minus El Niño years. Green shades show regions where La Niña induce wetter conditions and El Niño induce drier conditions, while regions in brown shades show the opposite effect, i.e. La Niña inducing drier conditions and El Niño inducing wetter conditions (image credit: IRI Data Library). In general, La Niña events tend to induce wetter conditions for many parts of the region, except for Borneo and Southern Sumatra. Note that this anomaly composite has been generated using limited number El Niño/La Niña occurrences between 1979 and 2016 and therefore should be interpreted with caution.
El Niño/La Niña
  • For El Niño/La Niña updates, ASMC assesses information provided by the World Meteorological Organization (WMO) and  various international climate centres, such as the Climate Prediction Center (CPC) US, the Bureau of Meteorology (BoM) Australia, as well information from the International Research Institute for Climate and Society (IRI) which contains model outputs from various other centres around the world. For more information on El Niño/La Niña, please refer to the FAQs website.