EI Niño/La Niña Status
Updated on 6 December 2023
The El Niño Southern Oscillation (ENSO) monitoring system state is “El Niño Conditions”. The oceanic indicators, including the Nino3.4 index, continue to show El Niño conditions, with key atmospheric indicators (cloudiness and trade winds) also supporting these conditions. The Nino3.4 index was 1.35°C for October 2023 and 1.18°C for the August – October 2023 three-month average.
El Niño conditions are predicted to continue until at least February-March 2024, with a gradual weakening of the El Niño from January 2024.
Short note on the Indian Ocean Dipole: The positive Indian Ocean Dipole (IOD) has likely reached its peak strength. Models predict the positive IOD to end by January-February 2024. A positive IOD typically results in below-average rainfall over Singapore and the nearby region.
Further Information on ENSO
ENSO conditions are monitored by analysing Pacific sea surface temperatures (SSTs), low level winds, cloudiness (using outgoing longwave radiation), and sub-surface temperatures. Special attention is given to SSTs, as they are one of the key indicators used to monitor ENSO. Here, three different datasets are used: HadISST, ERSSTv5, and COBE datasets. As globally, SSTs have gradually warmed over the last century under the influence of climate change, the SST values over the Nino3.4 will increasingly be magnified with time, and hence appear warmer than they should be. Therefore, this background trend is removed from the SST datasets (Turkington, Timbal, & Rahmat, 2018), before calculating SST anomalies using the climatology period 1976-2014. So far, there has been no noticeable background trend in the low-level winds or cloudiness.
El Niño (La Niña) conditions are associated with warmer (colder) SSTs in the central and eastern Pacific. The threshold for an El Niño (La Niña) in the Nino3.4 region is above 0.65°C (below -0.65°C). El Niño (La Niña) conditions also correspond to an increase (decrease) in cloudiness around or to the east of the international dateline (180°), with a decrease (increase) in cloudiness in the west. There is also a decrease (increase) in the trade winds in the eastern Pacific. Sub-surface temperatures in the eastern Pacific should also be warmer (colder) than average, to sustain the El Niño (La Niña) conditions.
For ENSO outlooks, information from the World Meteorological Organization (WMO) and 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 other centres around the world. Each centre uses different criteria, including different SST thresholds. Therefore, variations between centres on the current ENSO state should be expected, especially when conditions are borderline.
The sea surface temperatures (SSTs) over the tropical Pacific showed an El Niño pattern in October 2023 (Figure 1). The tropical Pacific SSTs were above average for the central and eastern tropical Pacific. For the Nino3.4 region (red box), the SSTs warmed slightly in October. Across the Indian Ocean, the western portion (solid black box) was above average, while the eastern portion (dashed black box) was below average, indicative of a positive Indian Ocean Dipole (IOD).
Figure 1: Detrended SST anomalies October 2023 with respect to 1976-2014 climatology using ERSST v5 data. Red (blue) shades show regions of relative warming (cooling). The tropical Pacific Ocean Nino3.4 Region is outlined in red. The Indian Ocean Dipole index is the difference between average SST anomalies over the western Indian Ocean (black solid box) and the eastern Indian Ocean (black dotted box).
Looking at the Nino3.4 index in Figure 2, throughout 2022, the 1-month Nino3.4 index was within the La Niña range. From the end of 2022 onwards, there was a gradual warming of the index, returning to the ENSO-neutral range by March 2023. Between March and June, the index continued to warm, but was within the ENSO-neutral range. Since July 2023, the Nino3.4 has exceeded the El Niño threshold. El Niño conditions are considered when the 1-month warm SST anomalies are above the orange threshold and either persist or are predicted to persist for at least four months, along with supporting atmospheric observations.
Figure 2: The Nino3.4 index using the 1-month SST anomalies. Warm anomalies (≥ +0.65; brown) correspond to El Niño conditions while cold anomalies (≤ -0.65; blue) correspond to La Niña conditions; otherwise neutral (> -0.65 and < +0.65; grey).
Model outlooks from Copernicus C3S (Figure 3), based on the Nino3.4 SST index, show that most models predict that El Niño conditions are nearing their peak. From January 2024, models predict the El Niño conditions to start to weaken. While there is a small chance of a return to neutral in early 2024, most models predict the Nino3.4 index remain above the El Niño threshold until at least March 2024. Models are predicting either a moderate or strong El Niño.
Figure 3: Forecasts of Nino3.4 index’s strength until April 2024 from various seasonal prediction models from international climate centres (grey lines). The solid blue and yellow lines note the La Niña and El Niño thresholds used by MSS, while the dotted lines note the thresholds used by some other international centres.
Historical ENSO Variability
To classify a historical El Niño event, the 3-month average Nino3.4 value must be above 0.65°C for 5 or more consecutive months. For La Niña events, the threshold is -0.65°C. Otherwise it is considered neutral. ENSO events with a peak value above 1.5°C (El Niño) or below -1.5°C (La Niña) are considered strong. Otherwise, the events are considered weak to moderate in strength. The following figure (Figure 4) shows the development of the Nino3.4 index for the most recent El Niño and La Niña events in comparison to other El Niño/La Niña events.
Figure 4: Three-month Nino3.4 index development and retreat of different El Niño (left)/La Niña (right) events since the 1960s. Recent El Niño and La Niña events are in red and purple, respectively.
Impact of El Niño/La Niña on Singapore
During the most of Northeast Monsoon months from December to March, as well as in November, there is little relationship between ENSO and rainfall over Singapore (Figure 5). This weak correlation indicates that the Nino3.4 index is not a good predictor of rainfall amount for Singapore during this time of year (Figures 5 and 6).
Figure 5: Correlation between total seasonal rainfall (averaged over 5 Singapore stations) and seasonal Nino3.4 index from 1961-2017 centred on the month indicated (e.g., for June’s value it corresponds to season May-June-July). The statistically significant correlations at the 95% level are underlined, at 99% level in red.
Figure 6: Singapore rainfall anomalies for November – January (as a percentage of departure from long-term rainfall average) arranged in the order from strong La Niña (left) to strong El Niño (right). Brown bars denote El Niño years’ anomalies, blue bars denote La Niña years’ anomalies, and grey bars denote ENSO neutral years’ anomalies.
Turkington, T., Timbal, B., & Rahmat, R. (2018). The impact of global warming on sea surface temperature based El Nino Southern Oscillation monitoring indices. International Journal of Climatology, 39(2).