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December 2025 Quick Look

Published: December 19, 2025

A monthly summary of the status of El Niño, La Niña, and the Southern Oscillation, or ENSO, based on the NINO3.4 index (120-170W, 5S-5N)

As of mid-December 2025, the equatorial Pacific is in a La Niña state, with sea surface temperatures in the Niño 3.4 region having crossed the La Niña threshold. The CCSR/IRI ENSO plume forecast places the probability of La Niña at 56% for Dec-Feb 2026. From Jan–Mar 2026 onward, conditions the forecasts begin shifting toward ENSO-neutral, which is forecast to become the dominant category. Neutral probabilities rise to 64% at the start of the year and remain the leading state through the forecast period ending in Aug–Oct 2026. El Niño probabilities stay very low, below 10% through Mar–May 2026, but gradually increase thereafter, reaching 14% in Apr–Jun, 26% in May–Jul, 35% in Jun–Aug, and 38% by Jul–Sep 2026.

Figures 1 ((the official CPC ENSO probability forecast) and 3 (the objective model-based IRI ENSO probability forecast) are often quite similar. However, occasionally they may differ noticeably. There can be several possible reasons for differences. One is the human forecasters, using their experience and judgment, may disagree to some degree with the models, which may have known biases. Another reason is the models are not run at the same time that the forecasters make their assessment, so that the starting ENSO conditions may be slightly different between the two times. The charts on this Quick Look page are updated at two different times of the month, typically about a week apart, with the IRI forecast run later. Also note that the CPC forecast starts on the previous season while the IRI forecast starts on the current season.
Click on the for more information on each figure.

Historically Speaking

    El Niño and La Niña events tend to develop during the period Apr-Jun and they
  • Tend to reach their maximum strength during October - February
  • Typically persist for 9-12 months, though occasionally persisting for up to 2 years
  • Typically recur every 2 to 7 years

IRI ENSO Forecast

IRI Technical ENSO Update and Model-Based Probabilistic ENSO Forecast

Published: December 19, 2025

Note: The SST anomalies cited below refer to the OISSTv2 SST data set, and not ERSSTv5. OISSTv2 is often used for real-time analysis and model initialization, while ERSSTv5 is used for retrospective official ENSO diagnosis because it is more homogeneous over time, allowing for more accurate comparisons among ENSO events that are years apart. These two products may differ, particularly during ENSO events. The difference between the two datasets may be as much as 0.5 °C. Additionally in some years, the ERSSTv5 may tend to be cooler than OISSTv2 in the context of warming trends, because ERSSTv5 is expressed relative to a base period that is updated every 5 years, while the base period of OISSTv2 is updated every 10 years. In February 2021, both datasets were updated to reflect the 1991-2020 climatology period.

Recent and Current Conditions

The SST anomaly in the NINO3.4 region during the Sep–Nov 2025 season was -0.53 °C, and for November, it was -0.68 °C. The most recent weekly average (week centered on December 10, 2025) of the NINO3.4 index was -0.7 °C. These values indicate that Pacific sea-surface temperature anomalies have reached the La Niña threshold and, although still weak, are now firmly within La Niña territory, signaling the development of cold conditions across the equatorial Pacific. The IRI’s definition of El Niño, similar to NOAA/Climate Prediction Center’s, requires that the monthly SST anomaly in the NINO3.4 region (5°S-5°N; 170°W-120°W) exceed +0.5 °C. Similarly, for La Niña, the anomaly must be -0.5 °C or colder.

By mid-December 2025, signs of La Niña conditions have been present in both the atmosphere and ocean. The Southern Oscillation Index (SOI) for November stood strong at +12.5, with the equatorial SOI at +0.7. Low-level winds (850 hPa) were easterly across the east-central and eastern Pacific. Enhanced convection and increased rainfall were evident over parts of Indonesia, marked by below-average OLR, while suppressed convection and reduced precipitation dominated around the Date Line with above-average OLR. Subsurface temperature anomalies have stayed negative since mid-July, with only a brief and modest peak in the past two months. Together, these patterns confirm the presence of La Niña conditions.

Expected Conditions

Note – Only models that produce a new ENSO prediction every month are considered in this statement.

The El Niño/Southern Oscillation (ENSO) Diagnostic Discussion, released on 11 December 2025 by the Climate Prediction Center (CPC)/NCEP/NWS, maintained a “La Niña Advisory” forecasting the presence of La Niña conditions that are favored to persist through December 2025 – February 2026, with a transition to ENSO-neutral most likely in January-March 2026 (68% chance).

The latest set of ENSO prediction models from mid-December 2025 is now available in the CCSR IRI ENSO prediction plume. These are used to assess the probabilities of the three ENSO categories by using the average value of the NINO3.4 SST anomaly predictions from all models in the plume, equally weighted. A standard Gaussian error is imposed over that averaged forecast, with its width determined by an estimate of overall expected model skill for the season of the year and the lead time. Higher skill results in a relatively narrower error distribution, while low skill results in an error distribution with width approaching that of the historical observed distribution.

According to the December 2025 CCSR/IRI ENSO plume forecast, the probability of La Niña conditions persisting during Dec–Feb (DJF) 2025/26 is 56%, while ENSO-neutral conditions are the next most likely outcome, with an estimated probability of 46%. From Jan–Mar through Aug–Oct 2026, the outlook favors ENSO-neutral conditions, with probabilities ranging from 85% to 44% across the overlapping seasonal periods. During this period, La Niña probabilities range from 35% to 8%, with the likelihood of El Niño gradually increasing from 1% to 38% by Jul-Sep 2026. A plot of the probabilities summarizes the forecast evolution. The climatological probabilities for La Niña, ENSO-neutral, and El Niño conditions vary seasonally, and are shown by the lines on the plot, and are given in a table at the bottom of this page for each 3-month season.

Caution is advised in interpreting the forecast distribution from the Gaussian standard error as the actual probabilities, due to differing biases and performance of the different models. In particular, this approach considers only the mean of the predictions, and not the total range across the models, nor the ensemble range within individual models. At longer leads, the skill of the models degrades, and uncertainty in skill must be convolved with the uncertainties from initial conditions and differing model physics, which leads to more climatological probabilities in the long-lead ENSO Outlook than might be suggested by the suite of models. Furthermore, the expected skill of one model versus another has not been established using uniform validation procedures, which may cause a difference in the true probability distribution.

It is worth noting that the Relative Oceanic Niño Index (RONI), which measures sea surface temperature anomalies in the eastern equatorial Pacific relative to the rest of the equatorial band, has consistently and increasingly exceeded the −0.5 La Niña threshold for the past several overlapping seasons. For Jul–Sep, Aug–Oct, and Sep–Nov 2025, the RONI was -0.63, -0.76, and -0.85 °C respectively The Pacific Decadal Oscillation (PDO) Index in November 2025 recorded a value of −1.67.

A caution regarding the model-based ENSO plume predictions (released mid-month) is that factors such as known specific model biases and recent changes in the tropical Pacific that the models may have missed, are not considered. This approach is purely objective. Those issues are taken into account in CPC’s official outlooks, which are issued early in the month, and which will include some human judgment in combination with the model guidance.

IRI ENSO Forecast Histogram Image
Season La Niña Neutral El Niño
DJF 56 44 0
JFM 34 65 1
FMA 18 79 3
MAM 8 85 7
AMJ 9 78 13
MJJ 10 64 26
JJA 12 53 35
JAS 15 50 35
ASO 18 44 38

ENSO Forecast

IRI ENSO Predictions Plume

Published: December 19, 2025

Note on interpreting model forecasts

The following graph and table show forecasts made by dynamical and statistical models for SST in the Nino 3.4 region for nine overlapping 3-month periods. Note that the expected skills of the models, based on historical performance, are not equal to one another. The skills also generally decrease as the lead time increases. Thirdly, forecasts made at some times of the year generally have higher skill than forecasts made at other times of the year--namely, they are better when made between June and December than when they are made between February and May. Differences among the forecasts of the models reflect both differences in model design, and actual uncertainty in the forecast of the possible future SST scenario.

Interactive Chart

You can highlight a specific model by hovering over it either on the chart or the legend. Selecting An item on the legend will toggle the visibility of the model on the page. You can also select DYN MODELS or STAT MODELS to toggle them all at once. Clicking on the "burger" menu above the legend will give you options to download the image or expand to full screen. If you have any feedback on this new feature, please let us know at webmaster@iri.columbia.edu.

List of Models Used

Forecast SST Anomalies (deg C) in the Nino 3.4 Region

Seasons (2025 – 2026)
Model DJF JFM FMA MAM AMJ MJJ JJA JAS ASO
Dynamical Models
AUS-ACCESS -0.27 0.10 0.43 0.73
AUS-RELATIVE -0.67 -0.33 0.00 0.30
BCC DIAP -0.32 -0.21 -0.07 0.01 0.11 0.23 0.42 0.57 0.68
COLA CCSM4 -0.33 -0.04 0.23 0.49 0.71 0.97 1.29 1.57 1.73
CS-IRI-MM -0.52 -0.21 0.05 0.21 0.38 0.57
IOCAS ICM -0.58 -0.51 -0.39 -0.22 -0.09 0.01 0.10 0.16 0.19
JMA -0.37 -0.17 -0.02 0.10 0.25
KMA -0.42 -0.13 0.12 0.34
LDEO -0.52 -0.42 -0.34 -0.29 -0.23 -0.16 -0.12 -0.18 -0.29
MetFRANCE -0.78 -0.56 -0.31 -0.06 0.19
NASA GMAO -0.72 -0.42 -0.08 0.18 0.41 0.66 0.91
NCEP CFSv2 -0.35 -0.07 0.14 0.33 0.46 0.57 0.70
SINTEX-F -0.40 -0.15 0.08 0.27 0.46 0.67 0.83 0.90 0.90
UKMO -0.57 -0.29 0.05 0.31
Average, Dynamical models -0.487 -0.244 -0.007 0.194 0.265 0.440 0.590 0.603 0.643
Statistical Models
BCC STATISTICAL -0.72 -0.62 -0.48 -0.37 -0.26 -0.16 -0.10 -0.11 -0.14
CPC CA -0.50 -0.32 -0.13 0.01 0.26 0.41 0.51 0.53 0.55
CPC MRKOV -0.98 -0.83 -0.71 -0.59 -0.48 -0.40 -0.34 -0.28 -0.22
CSU CLIPR -0.58 -0.52 -0.45 -0.39 -0.38 -0.38 -0.37 -0.38 -0.39
IAP-NN -0.57 -0.45 -0.29 -0.13 0.03 0.17 0.29 0.37 0.41
NTU CODA -0.76 -0.68 -0.59 -0.55 -0.53 -0.43 -0.39 -0.55 -0.72
TONGJI-ML -0.63 -0.68 -0.65 -0.46 -0.28 -0.05 0.02 0.21 0.29
UCLA-TCD -0.42 -0.28 -0.10 0.09 0.26 0.38 0.45 0.46 0.43
UW PSL-CSLIM -0.51 -0.29 -0.04 0.19 0.37 0.48 0.51 0.50 0.50
UW PSL-LIM -0.52 -0.41 -0.35 -0.29 -0.21 -0.12 -0.03 0.04 0.09
XRO -0.68 -0.62 -0.52 -0.40 -0.28 -0.17 -0.09 -0.03 0.00
Average, Statistical models -0.624 -0.518 -0.393 -0.263 -0.137 -0.024 0.042 0.068 0.073
Average, All models -0.547 -0.364 -0.177 -0.007 0.055 0.171 0.255 0.235 0.251

Discussion of Current Forecasts

The IRI ENSO prediction plume indicates a moderate likelihood of La Niña conditions during Dec–Feb 2025/26, with a 56% chance. The multimodel mean of statistical and dynamical models suggests La Niña conditions are likely to transition to ENSO-neutral in Jan-Mar 2026 (64%), and ENSO-neutral conditions are expected to become dominant once again. During this period, the chances of El Niño development remain minimal through the first quarter of 2026, but then gradually rise, reaching to a highest probability of 38% in Aug-Oct 2026. However, such long-lead forecasts remain highly uncertain, as they pass through the spring predictability barrier. Based on the multi-model mean (Dynamical andStatistical models) prediction, and the expected skill of the models by start time and lead time, the probabilities (in %) for La Niña, ENSO-neutral and El Niño conditions (using -0.5 °C and 0.5 °C thresholds) over the coming 9 seasons are:

Season La Niña Neutral El Niño
DJF 56 44 0
JFM 34 65 1
FMA 18 79 3
MAM 8 85 7
AMJ 9 78 13
MJJ 10 64 26
JJA 12 53 35
JAS 15 50 35
ASO 18 44 38

Summary of forecasts issued over last 22 months

The following interactive plot shows the model forecasts issued not only from the current month (as in the plot above), but also from the 21 months previous to this month. The observations are shown up to the most recently completed 3-month period. The plots allow comparison of plumes from the previous start times, or examination of the forecast behavior of a given model over time.
Hovering over any single model will highlight that particular model in the chart.
Clicking a particular model will hide/show that model in the chart.
At the bottom of the plot, you can select which models to show in the chart: all the models, the dynamical models only, or the statistical models only.

Notes on the data 

Only models producing forecasts on a monthly basis are included. This means that some models whose forecasts appear in the Experimental Long-Lead Forecast Bulletin (produced by COLA) do not appear in the table.

Once an IRI ENSO probability forecast has been published, the results stand even if a model reports an error and changes their data. When this happens we will update the plume with the model's correct values even though our forecast hasn't changed. What this means is that our forecast is always the same, but the underlying data may be different from what we based our forecast on.

The SST anomaly forecasts are for the 3-month periods shown, and are for the Nino 3.4 region (120-170W, 5N-5S). Often, the anomalies are provided directly in a graph or a table by the respective forecasting centers for the Nino 3.4 region. In some cases, however, they are given for 1-month periods, for 3-month periods that skip some of the periods in the above table, and/or only for a region (or regions) other than Nino 3.4. In these cases, the following means are used to obtain the needed anomalies for the table:

  • Temporal averaging
  • Linear temporal interpolation
  • Visual averaging of values on a contoured map

The anomalies shown are those with respect to the base period used to define the normals, which vary among the groups producing model forecasts. They have not been adjusted to anomalies with respect to a common base period. Discrepancies among the climatological SST resulting from differing base periods may be as high as a quarter of a degree C in the worst cases. Forecasters are encouraged to use the standard 1991-2020 period as the base period, or a period not very different from it.

ENSO Forecast

Forecast Probability Distribution Based on the IRI ENSO Prediction Plume

Published: December 19, 2025

The plots on this page show predictions of seasonal (3-month average) sea surface temperature (SST) anomaly in the Niño3.4 region in the east-central tropical Pacific (5°N-5°S, 120°-170°W), covering the nine overlapping seasons beginning with the current month. The predictions are based on the large (20+) set of dynamical and statistical models in the plume of model ENSO predictions.

  • Model Based Prediction Percentiles Image

    Figure 5

    Predictions of ENSO are probabilistic. The ensemble mean prediction is only a best single guess. On either side of that prediction, there is a substantial uncertainty distribution, or error tolerance. The second plot (Figure 2) shows the estimated probability distribution of the predictions, showing a set of percentiles within that distribution for each lead time. The distribution is modeled as a normal (Gaussian) distribution, so that the overall mean forecast represents the center, or 50 percentile, in the distribution. The overall mean is formed using equal weighting among all models. On either side, other percentile values are shown symmetrically, ranging from 1 to 99 and including some intermediate percentiles (5 and 95, 15 and 85, and 25 and 75). The plot enables a user to estimate the probability of the Niño3.4 SST anomaly to be greater or less than some critical value, or within some interval. If, for example, the 85 percentile falls at 1.8° C above average, the probability of the SST exceeding 1.8° C can be estimated at 15%. Probabilities for exceeding or not exceeding values not exactly on percentile line can be roughly interpolated by eye. The overall width of the probability distribution is derived from the historical skill of the hindcasts of the models, from 1982 to present, for the specific forecast start time and lead time. This method of defining the probability distribution represents one of two general approaches, the other approach being a direct counting of ensemble members within each of the percentile bands. This second approach assumes that the ensemble spreads of the models are true representations of the uncertainty. Individual model spreads have often been found to be somwehate narrower than they should be, although in multi-model ensembles this tendency has been shown to be milder or even eliminated.

  • Model Based Prediction Distribution Image

    Figure 6

    Figure 6, sometimes called a spaghetti diagram, shows synthetically generated prediction scenarios that are equally likely. Here, 100 scenarios are shown; any number can be generated for such a diagram. Each scenario is produced using a random number generator, combined with knowledge of the mean forecast and its uncertainty, as well as the amount of persistence of anomalies. The degree of persistence of anomalies is based on the correlation of prediction errors from one lead time to another. In other words, the individual lines are designed to show the correct amount of persistence as expected in nature, rather than jumping around more randomly from one lead time to the next. The uncertainty and persistence statistics are based on the set of 7 NMME (North American Multimodel Ensemble) models, as it is assumed that these statistics are approximately applicable to all of the models. Sometimes the “spaghetti density” may appear asymmetric about the mean of all the forecasts or outside of the 85 and 15 percentile lines. This is purely sampling variability, and would not occur if many thousands of such lines were plotted. But with that many lines, most of the plot would be too crowded to get a sense of the behavior of the lines near the center of the distribution. The main purpose of the diagram is to serve users who want to assess realistic individual scenarios of ENSO behavior rather than statistical summaries of the forecast like the percentiles shown in the second plot.

IOD Forecast

Published: December 19, 2025

Note: The Dipole Mode Index is calculated based on the ERSSTv5 data. To account for evolving background conditions and long-term warming, SST anomalies were calculated relative to a sliding monthly climatology. For each month in the time series, the climatology was computed as the mean SST for that calendar month over the prior 30 years. The Dipole Mode Index (DMI) is then defined as the difference in sea surface temperature anomalies between the western equatorial Indian Ocean (50°E–70°E, 10°S–10°N) and the southeastern equatorial Indian Ocean (90°E–110°E, 10°S–0°), and is used to quantify the strength and phase of the Indian Ocean Dipole (IOD).

Current Conditions

In November 2025, the Dipole Mode Index measured –0.74 °C, signaling the continued persistence of negative IOD conditions across the Indian Ocean. According to the CCSR@NASA-GISS/IRI’s criteria for defining positive and negative Indian Ocean Dipole (IOD) events, a positive IOD phase is defined when the DMI exceeds +0.4 °C, and a negative IOD when it falls below −0.4 °C. The IOD is considered inactive (neutral) when the DMI lies between −0.4 °C and +0.4 °C.

Model-Based IOD Outlook: Deterministic Forecasts from the NMME

Forecasts from the latest set of operational models in the North American Multi-Model Ensemble (NMME) project are used to construct deterministic IOD forecasts from each individual model using its ensemble mean DMI to form an IOD forecast plume. The IOD plume plot shows the latest set of predictions from CESM1, CFSv2, CanESM5, GEM-NEMO, NASA, GFDL-SPEAR, along with their equally weighted multi-model mean (MME). The observed Dipole Mode Index (DMI; shown in black) exhibits a consistent downward trend from May to November 2025, transitioning into negative IOD conditions by late August and reaching its most negative value (peak intensity of the negative phase) in October 2025. Forecasts for December 2025 exhibit considerable spread across individual plume models: three models predict persistence of negative IOD conditions (DMI below −0.4°C), while the other three forecast a transition to neutral conditions (DMI warmer than −0.4°C). The equally weighted multi-model ensemble (MME) mean lies near the borderline of the negative IOD threshold (−0.4°C), highlighting uncertainty in the IOD evolution during this transition month. Beyond December 2025, neutral IOD conditions are expected to dominate throughout the subsequent forecast period.

Probabilistic IOD Forecasts from the NMME

Based on December 2025 initialization data, the model-based probabilistic forecast of the Indian Ocean Dipole was generated by CCSR@NASA-GISS/IRI to assess potential phase developments. Probabilities are computed using a counting method, where each ensemble member from the contributing models is evaluated individually, and pooled to determine the likelihood of a negative, neutral, or positive IOD phase for the upcoming months. Climatological probabilities for each IOD phase, based on historical data, are shown as dotted lines for reference.

The forecast for December 2025 is nearly evenly divided between maintaining negative IOD conditions and transitioning to neutral conditions. Neutral probabilities rise sharply thereafter, remaining dominant throughout the forecast period (January–June 2026). Positive IOD probabilities stay very low, around 20% during spring 2026.

In summary, the forecast suggests a likely continuation of the negative IOD event in December 2025, followed by a rapid transition toward neutral IOD conditions.

December 19, 2025 IOD Model Based Forecast
Historical SST Anomalies Image

References

Real-time ENSO forecast skill evaluated over the last two decades, with focus on the onset of ENSO events. Ehsan, M.A., L’Heureux, M.L., Tippett, M.K., Robertson, A.W, Turmelle, J.P., npj Clim Atmos Sci, 2024.

The IRI ENSO forecast is released on the 19th of each month. If the 19th falls on a weekend or holiday, it is released on the closest business day.

Forecast and model data used in our probabilistic forecast can be accessed by submitting a Request to Access IRI ENSO Data.

All data from this website is covered under the Creative Commons Attribution 4.0 License. When citing IRI ENSO images or data, please use "Images [or Data] provided by The International Research Institute for Climate and Society, Columbia University Climate School", with a link to https://iri.columbia.edu/ENSO.