Updated on 21 December 2016

In November 2016, the cooling of the equatorial Pacific Ocean’s sea-surface temperature (SST) Niño3.4 region weakened and the anomaly for that month had returned to neutral (Figure A). Atmospheric variables, such as trade winds and cloudiness, over the equatorial Pacific showed borderline and weakening La Niña conditions. The Niño3.4 index for November 2016 was -0.42 (Figure B). The latest 3-month average (September-November) of -0.53 had weakened slightly from the previous value but is still within the threshold for weak La Niña. There were patches of observed wetter-than-normal, large scale rainfall anomalies for the region in November 2016 (Figure C) but not as widespread as that in October 2016.

Climate models do not significantly favour La Niña over neutral conditions in the Dec-Feb 2016-17 season (Figure D) and the cool anomalies are predicted to weaken from then on (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: On average the tropical Pacific Ocean Niño3.4 region (red box, 120°W-170°W and 5°S-5°N) was cooler than normal but had weakened to neutral for November 2016 (image credit: IRI Map Room). Warm shades show regions of relative warming, while cool shades show regions of relative cooling with respect to 1971-2000 climatology for that month.

 

    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 Dec 2015 to Nov 2016 (image credit: IRI Map Room). Both SST and atmospheric responses over the tropical Pacific Ocean indicate weakening of La Niña conditions.

 

    Figure C: Spatial rainfall anomaly patterns in the region for November 2016 where patches of wetter-than-normal, large scale rainfall anomalies for the region were observed but not as widespread as October 2016 (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 later part of 2016 and first half of 2017. La Niña is not significantly favoured over neutral conditions during Dec-Feb 2016-2017 (image credit: IRI-CPC).

 

    Figure E: Forecasts of Niño3.4 index’s strength for the later part of 2016 and 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 from Dec-Feb 2016-2017 season onwards (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.