EI Niño/La Niña Status
Updated on 14 October 2025
The El Niño Southern Oscillation (ENSO) monitoring system state is “La Niña Watch”. The Nino3.4 index passed the La Niña threshold in September 2025. However, key atmospheric indicators (cloudiness and trade winds in the central Pacific) indicated neutral or weak La Niña-like conditions in September 2025. The Nino3.4 index was -0.81°C for September 2025 and -0.63°C for the July – September 2025 three-month average.
La Nina conditions are predicted for October – December 2025, with some models predicting the La Nina conditions to last until March 2026.
Short note on the Indian Ocean Dipole: A negative Indian Ocean Dipole (IOD) is present. The negative IOD is predicted to persist until December 2025.
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 in September 2025 were below average in the central and eastern portions of the region and above average in the west (Figure 1). The coolest (negative) anomalies were around the eastern half of the Nino3.4 region (red box). Across the Indian Ocean, the equatorial region was above average in the eastern parts of the region (including the dashed black box) and below to near-average in the west. This dipole pattern is indicative of a negative IOD.
Figure 1: Detrended SST anomalies for September 2025 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, the 1-month Nino3.4 index was within the neutral range for much of 2024, with a gradual cooling of the index and approaching the La Niña threshold. The index passed the La Niña threshold in December 2024 and returned to ENSO neutral in March 2025. The Nino3.4 index was then negative, but within the ENSO neutral range, until September 2025, when it passed the La Niña threshold again. For La Niña conditions to be present, 1-month cold SST anomalies (observed or forecast) should persist for at least four months below the threshold, with at least one of the months observed along 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 models predict La Niña conditions until the end of 2025. From January 2026 onwards, the models predict a weakening of the index and a gradual return to neutral conditions. Most predict a return to neutral by March 2026. The developing La Niña conditions are predicted to be weak or moderate.
Figure 3: Forecasts of Nino3.4 index’s strength until March 2025 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 October, as well as the Southwest Monsoon season (June to September), the correlation of ENSO with rainfall over Singapore is strong (Figure 5), i.e. if an El Niño or La Niña conditions are present, the rainfall patterns are likely to be influenced, particularly by a moderate or strong event. During November and much of the Northeast Monsoon months from December to March, there is little relationship between ENSO and rainfall over Singapore. This weak correlation indicates that the Nino3.4 index is not a good predictor of rainfall amount for Singapore during this time of year (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.
References
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).