For September 2016, the equatorial Pacific Ocean’s sea-surface temperature (SST) anomaly over the Nino3.4 region was cooler than average at borderline La Niña threshold values (Figure A). Atmospheric variables, such as trade winds and cloudiness, over the equatorial Pacific indicate only weak signs of developing La Niña conditions. The Niño3.4 index for September 2016 was -0.53 (Figure B) and the latest 3-month average (July-September) is -0.44, which is still outside the -0.5 weak La Niña threshold. There were observed wetter -than-normal, large scale rainfall anomalies for the region in September 2016 (Figure C).
Experts assessing international climate models have maintained the probability of La Niña occurring at 60% chance and developing in the October – December season (Figure D) with weak or borderline La Niña being most likely (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, especially for the southern parts of the region (Maritime Continent) during June to October (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 events induced more significant changes in rainfall than the stronger events.
- Figure A: On average the tropical Pacific Ocean region was cooler than average at borderline La Niña threshold values over the Niño3.4 region (red box, 120°W-170°W and 5°S-5°N) in September 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 Nov 2015 to Sep 2016 (image credit: IRI Map Room). Both SST and atmospheric responses over the tropical Pacific Ocean indicate only weak signs of developing La Niña conditions.
- Figure C: Spatial rainfall anomaly patterns in the region for September 2016 (image credit: IRI Map Room). Brown (green) shades show drier (wetter) than the average climatological rainfall for August (1970 – 2009). There were observed wetter-than-normal, large scale rainfall anomalies for the region in September 2016. 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 conditions are favoured over neutral conditions during this period (image credit: IRI-CPC).
- Figure E: Forecasts of Niño3.4 index’s strength for later part of 2016 and first half 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 possibility of weak or borderline La Niña conditions establishing in the later part of 2016 (image credit: IRI-CPC).
- Figure F: June to October rainfall anomaly composite for La Niña years minus El Niño years. In general, 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). Note that this anomaly composite has been generated using limited number El Niño/La Niña occurrences between 1979 and 2015 and therefore should be interpreted with caution.
El Niño/La Niña
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.
Frequently Asked Question
What is El Niño/La Niña and how do they affect weather in South East Asia?
In South East Asia, higher than normal rainfall tends to occur during a La Niña episode which may result in an increased occurrence of floods.
The correlation between El Niño/La Niña and its associated weather impacts on South East Asia differ from one place to another and for different seasons.
The image above shows the precipitation anomalies averaged over the El Niño and La Niña years. For instance, the impact of El Niño is typically stronger over the southern and eastern part of South East Asia during the months of Jun – Oct.