EI Niño/La Niña Status
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 -0.53had 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 Singapore
Singapore would normally experience wetter and cooler conditions during La Niña events, especially during the Southwest Monsoon period (June – September), including October. The opposite, i.e. drier conditions over Singapore, usually occurs during El Niño events. Outside this season, the impact of El Niño/La Niña is less significant for Singapore (Figure F and Figure G). For example during the Northeast Monsoon season (December to early March), the impact on rainfall from El Niño/La Niña is less pronounced.
No two El Niño events or two La Niña events are alike in terms of their impact on Singapore’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 during the Southwest Monsoon season than the stronger events (Figure H).
For El Niño/La Niña updates, MSS 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.
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: Correlation between total monthly rainfall (averaged over 28 Singapore stations) and Niño3.4 index from 1980-2013. It shows statistically significant (red) negative correlations between local rainfall and Niño3.4 in July, September and October, which suggest that warmer temperatures in the Niño3.4 region lead to significantly less rainfall over Singapore and vice versa. In other months, where the correlations are weaker or insignificant, the relationship is not as established.
Figure G: Correlation between total seasonal rainfall (averaged over 28 Singapore stations) and seasonal Niño3.4 index (also known as Oceanic Niño Index, ONI) from 1980-2013. It shows statistically significant (red) negative correlations between local rainfall and the ONI during JAS and ASO, which suggest that warmer temperatures in the Niño3.4 region lead to significantly less rainfall over Singapore and vice versa during these seasons. In other seasons, where the correlations are weaker or insignificant, the relationship is not as established.
Figure H: Singapore rainfall anomalies for June-September (as percentage of departure from long-term rainfall average) arranged in the order from strong La Niña (left) to strong El Niño (right). Warm shades denote El Niño years, cool shades denote La Niña years (La Niña is the opposite of El Niño) and white denotes neutral years. WL, ML and SL refer to weak, moderate and strong La Niña respectively, while WE, ME and SE refer to weak, moderate and strong El Niño respectively.