In May, the Niño 3.4 index dropped to below the 0.5 threshold value and thus fell into the neutral category. Sea-surface temperature (SST) anomalies over some parts of the tropical Pacific Ocean were already near zero or even positive by then (Figure A). The Niño 3.4 index for May 2016 was 0.38 (Figure B) and the latest 3-month average (Mar-May) dipped further from 1.8 to 1.1. The large-scale atmosphere was also in near-neutral conditions with near-average wind and convection activities across the equatorial Pacific Ocean. These observations signal the end of the current El Niño event.
The characteristic large scale, drier-than-normal rainfall response to El Niño over the Southeast Asia region was not observed generally (Figure C), which was consistent with the waning El Niño signal. International climate models and expert assessment predict that La Niña conditions are likely for the second half of 2016 (Figure D) with about 70% chance of it developing by the August-October season (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 was in neutral conditions over the Niño3.4 region (red box, 120°W-170°W and 5°S-5°N) in May 2016 (image credit: IRI Map Room). Warm colour shades show regions of relative warming, while cool colour 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 Jun 2015 to May 2016 (image credit: IRI Map Room). Both this and atmospheric responses over the tropical Pacific Ocean indicate the end of El Niño and the onset of neutral conditions.
- Figure C: Spatial rainfall anomaly patterns in the region for May 2016 (image credit: IRI Map Room). Brown (green) colour shades show drier (wetter) than the average climatological rainfall for May (1970 – 2009). In general, the characteristic large-scale drying due to El Niño is not observed; consistent with the wading El Niño signal. Quantitative anomaly values are only indicative due to limitations in the data source.
- Figure D: Forecasts of Niño3.4 index’s strength for second half of 2016 and early 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 La Niña conditions occurring in the second half of 2016 (image credit: IRI-CPC).
- Figure E: Probability of El Niño (red), La Niña (blue) and neutral conditions (green) for second half of 2016 and early 2017. La Niña conditions are favoured over neutral conditions during this period (image credit: IRI-CPC).
- Figure F: June to October rainfall anomaly composite for La Niña years minus El Niño years. In general, green colour 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 the anomaly composite have been put together with 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.