Updated on 25 May 2018

The sea surface temperature (SST) in the tropical Pacific Ocean were within neutral values in April 2018 over the Nino3.4 region (Figure A). Most of the atmospheric indicators of El Niño/La Niña were also indicating neutral conditions. The 1-month Nino3.4 value for April 2018 was -0.3 and the 3-month average (February to April 2018) Nino3.4 was -0.5 (Figure B). Partial data in May 2018 showed further weakening of the SST cold anomalies towards climatological values.

Models indicate that the tropical Pacific Ocean SST anomalies will continue to warm (Figure C) with more than 60% chance of neutral conditions for the May-July season in progress and up to the Jun-August season (Figure D). Some models indicate the possibility of a weak and late 2018 El Niño developing by year’s end but others do not. At present, the probability of an El Niño event occurring late in the year is hardly larger than the system remaining in a neutral state.

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 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.

Sea-surface temperature anomaly over the Pacific and Indian Oceans.

    Figure A: Sea-surface temperature (SST) anomalies for April 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 still colder than average in April 2018 but the cold anomalies are weakening. 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). While the Indian Ocean Dipole Mode index (WTIO minus SETIO) was positive it is still within neutral values. Data source: ERSSTv4 from NOAA.

 

Observed Nino3.4 index

    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.

 

Forecast Nino3.4 index

    Figure C: Forecasts of Nino3.4 index’s strength for 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 May-July season in progress and with a range of possible outcomes by year’s end including weak, late El Niño developing (image credit: IRI-CPC).

 

Probabilistic Nino3.4 Outlook

    Figure D: Probability of El Niño (red), La Niña (blue) and neutral conditions (grey) for 2018. Neutral conditions are likely for the May-July 2018 season in progress until late in 2018 when El Niño conditions are slightly more favoured (image credit: IRI-CPC).

 

June to October rainfall anomaly compositeRainfall scale

    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).

 

November to January rainfall anomaly compositeRainfall scale

    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.