- EI Niño/La Niña Status
EI Niño/La Niña Status
Updated on 5 May 2023
The El Niño Southern Oscillation (ENSO) monitoring system state is “Neutral”. The Nino3.4 index currently indicates ENSO-neutral conditions, along with the atmospheric indicators (cloudiness and wind anomalies). However, there are signs in the tropical Pacific that support El Niño conditions developing in the next few months (e.g., warmer subsurface ocean temperatures). The Nino3.4 index was -0.33°C for March 2023 and 0.64°C for the January – March 2023 three-month average.
Models predict ENSO-neutral conditions to continue during May-June 2023 and El Niño conditions to develop from July-August 2023. However, there is still a chance of ENSO-neutral conditions in the second half of 2023 as models have lower accuracy at this time of the year.
Short note on the Indian Ocean Dipole: The Indian Ocean Dipole (IOD) is in neutral phase. Most models predict a positive IOD to develop from middle of 2023.
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 central and eastern tropical Pacific overall represented ENSO-neutral conditions in March 2023 (Figure 1) The SSTs continued to warm in March, although still were cooler than average in the Nino3.4 region (red box). Across the Indian Ocean, while the SSTs are cooler than average, the eastern portion is only slightly cooler than the western portion, indicating that the Indian Ocean Dipole is neutral.
Figure 1: Detrended SST anomalies for March 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, starting in 2021, there was a prolonged period of the 1-month Nino3.4 index being within the La Niña range. From the end of 2022 onwards, there has been a gradually warming of the index, returning to the ENSO-neutral range by March 2023. La Niña conditions are considered present when the 1-month cold SST anomalies (observed or forecast) persist or are predicted to persist for at least four months below the threshold, along with supporting atmospheric observations. La Niña conditions are considered to have ended when the 1-month SST anomalies are above the threshold, as well as atmospheric conditions no longer indicate La Niña conditions.
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 models predict ENSO neutral conditions are likely to continue in April and May 2023. From June, models predict an increase in the chance of El Niño conditions, with models predicting either ENSO neutral or El Niño conditions in July and August 2023, although there is considerable uncertainty in the long-term forecasts at this time of the year.
Figure 3: Forecasts of Nino3.4 index’s strength until September 2023 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
Towards the end of the Northeast Monsoon season and into the first inter-monsoon period, ENSO has a small influence on Singapore’s rainfall (Figure 5). Between February and May, La Niña events tend to bring wetter conditions than El Niño events, although there is still a lot of year-to-year variability (Figure 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 June – October (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).