The sea surface temperature (SST) anomalies in the tropical Pacific Ocean were within neutral values in June 2018 over the Nino3.4 region (Figure A). Likewise, most of the atmospheric indicators of El Niño/La Niña were indicating neutral conditions. The 1-month Nino3.4 value for June 2018 was +0.1 and the 3-month (April to June 2018) average Nino3.4 was zero (Figure B).
Models indicate that the tropical Pacific Ocean SST anomalies will continue to warm (Figure C) but are more likely to remain neutral for the July-September season in-progress (Figure D). Some models indicate the possibility of a weak and late 2018 El Niño developing, with a higher risk of occurrence from the October-December season onwards.
Impact of El Niño/La Niña on Southeast Asia
Typically the impact from El Niño for Southeast Asia is drier-than-normal rainfall conditions, especially during the Southwest Monsoon period (June – September), including October (Figure E) and especially over the Maritime Continent. Warmer conditions typically follow drier periods. During La Niña events the opposite, i.e. wetter-than-normal conditions, normally occurs. For November – January season, the impact of El Niño/La Niña is less coherent for some parts of the region, for example over mainland Southeast Asia, Borneo, southern Sumatra, and the Malay Peninsula (Figure F). 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 had more impact on rainfall during the Southwest Monsoon season than the stronger events, but this could be contributed by other factors as well.
- Figure A: Sea-surface temperature (SST) anomalies for June 2018 with respect to 1981-2010 climatology. Warm shades show regions of relative warming, while cool shades show regions of relative cooling. The tropical Pacific Ocean Nino3.4 region (solid red box, 120°W-170°W and 5°S-5°N) was close to zero. The western Indian Ocean, WTIO (solid black box, 50°E-70°E and 10°S-10°N) was slightly warmer compared to the south-eastern Indian Ocean, SETIO (dotted black box, 90°E-110°E and 10°S-0°N), thus the Indian Ocean Dipole Mode index (WTIO minus SETIO) was still within neutral values. Data source: ERSSTv4 from NOAA.
- Figure B: The Nino3.4 index using the three-month running means of SST anomalies (against 1981-2010 base period) in the Nino3.4 region bounded by 5°N to 5°S and 170°W to 120°W. Warm anomalies (≥ +0.5) correspond to El Niño conditions while cold anomalies (≤ -0.5) correspond to La Niña conditions; otherwise neutral (> -0.5 and < +0.5). The horizontal axis is labelled with the first letters of the 3-month seasons, e.g. JFM refers to January, February, and March seasonal average. Data source: ERSSTv4 from NOAA.
- Figure C: Forecasts of Nino3.4 index’s strength for second half of 2018 and early 2019 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 Nino3.4 index to be within neutral values in the July-September season in-progress and with a range of possible outcomes by year’s end including weak, late El Niño developing (image credit: IRI-CPC).
- Figure D: Probability of El Niño (red), La Niña (blue) and neutral conditions (grey) for 2018. Neutral conditions are likely for the July-September 2018 season in-progress until later in 2018 when El Niño conditions are slightly more favoured (image credit: IRI-CPC).
- Figure E: June to October rainfall anomaly composite for El Niño years minus La Niña years. Brown shades show regions where El Niño induce drier conditions and La Niña induce wetter conditions, while regions in green shades show the opposite effect, i.e. El Niño inducing wetter conditions and La Niña inducing drier conditions (image credit: IRI Data Library). Note that this anomaly composite was generated using a limited number of El Niño/La Niña occurrences between 1979 and 2016 and therefore should be interpreted with caution (data: NOAA CPC CAMS_OPI).
- 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 a limited number of 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, information provided by the World Meteorological Organization (WMO) and various international climate centres are assessed. The centres include 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 consolidates model outputs from various other centres around the world.
Frequently Asked Questions
What is El Niño/La Niña and how do they affect weather in South East Asia?
The El Niño phenomenon is a non-regular occurrence in the tropical pacific region where warmer waters develop over the Eastern Tropical Pacific Ocean along the coast of South America. In South East Asia, this brings drier weather and increases the risk of forest fires and smoke haze. The La Niña phenomenon is the reverse of the El Niño where cooler waters develop over the Eastern Tropical Pacific Ocean along the coast of South America.
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.