EI Niño/La Niña Status
Updated on 01 February 2018
Warm sea surface temperature (SST) anomalies over the Nino3.4 region are still present (Figure A) but weakening. The 1-month Nino3.4 value for December 2018 was 0.9 (dipped from the previous monthly value of 1.0) while the 3-month (October to December 2018) average Nino3.4 was 1.0 (Figure B). The preliminary Nino3.4 value for January 2019 (partial month) fell significantly to below 0.5. Furthermore, temperatures beneath the ocean surface continue to show cooling trends since December 2018, especially for the central and eastern equatorial Pacific. Atmospheric indicators (e.g. outgoing longwave radiation, and trade winds) have not responded to the recent positive anomalies and remained weak or non-existent.
Models predict the tropical Pacific Ocean SST anomalies over the Nino3.4 will weaken further (Figure C). Overall, a continued return to ENSO-neutral conditions is expected in the coming months (Figure D).
Impact of El Niño/La Niña on Singapore
Singapore would normally experience drier and warmer conditions during El Niño events, especially during the period between June and October (Figure E and Figure F). The impact is more significantly felt during strong or moderate intensity events. The opposite, i.e. wetter conditions over Singapore, usually occurs during La Niña events. Outside the June to October season, the impact of El Niño/La Niña is less significant for Singapore. For example during the Northeast Monsoon season (December to early March), the impact on rainfall from El Niño/La Niña is less pronounced (Figure E and Figure F).
No two El Niño events or two La Niña events are alike in terms of their impacts 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 had more impact on rainfall during the June to October period than the stronger events, but this could be contributed by other factors as well (Figure G).
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) USA, the Bureau of Meteorology (BoM) Australia, as well as information from the International Research Institute for Climate and Society (IRI) which consolidates model outputs from various other centres around the world.
Figure A: Sea-surface temperature (SST) anomalies for December 2018 with respect to 1976-2014 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) show warm anomalies remain in December 2018. The western Indian Ocean, WTIO (solid black box, 50°E-70°E and 10°S-10°N) was warmer compared to the south-eastern Indian Ocean, SETIO (dotted black box, 90°E-110°E and 10°S-0°N). The Indian Ocean Dipole Mode index (WTIO minus SETIO) although positive is within neutral. Data source: ERSSTv5 from NOAA.
Figure B: The Nino3.4 index using the three-month running means of SST anomalies (against 1976-2014 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: ERSSTv5 from NOAA.
Figure C: Forecasts of Nino3.4 index’s strength for 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 weaken in the coming months (image credit: IRI-CPC).
Figure D: Probability of El Niño (red), La Niña (blue) and neutral conditions (grey) for 2019. Models significantly favour continued return to neutral conditions in the coming months. (image credit: IRI-CPC).
Figure E: Correlation between total monthly rainfall (averaged over 28 Singapore stations) and Nino3.4 index from 1980-2013. It shows statistically significant (red) negative correlations between local rainfall and Nino3.4 in July, September, and October, which suggest that warmer temperatures in the Nino3.4 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 F: Correlation between total seasonal rainfall (averaged over 28 Singapore stations) and seasonal Nino3.4 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 Nino3.4 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 G: Singapore rainfall anomalies for June-September (as a 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.