El Niño-Southern Oscillation (ENSO) Conditions and Alerts

The update occurs twice a month: early-month for Section I and mid-month for Section II & III.
IRI's Monthly Ouick Look updates to the lastest of the two.



I) CPC Official Probabilistic Forecast
(based on a consensus of NOAA's CPC and Columbia University's IRI forecasters, using observational information and model output, along with human judgment):

December 12, 2024  (updated early-month)

Alert Status:   La Niña Watch

La Niña conditions are most likely to emerge in November 2024 - January 2025 (59% chance), with a transition to ENSO-neutral most likely by March-May 2025 (61% chance).


DIAGNOSTIC DISCUSSION:

ENSO-neutral continued in November 2024, with near-average sea surface temperatures (SSTs) observed across the central and eastern equatorial Pacific Ocean central and eastern equatorial Pacific Ocean. Similar to the last couple of months, the latest weekly Niño indices ranged from +0.1°C (Niño-1+2) to -0.4°C (Niño-3). Below-average subsurface ocean temperatures persisted across the east-central and eastern equatorial Pacific Ocean.

Over the western and central equatorial Pacific, low-level wind anomalies were easterly and upper-level wind anomalies were westerly. Convection was suppressed over the Date Line and was enhanced over western Indonesia. The traditional and equatorial Southern Oscillation indices were positive. Collectively, the coupled ocean-atmosphere system reflected ENSO-neutral.

The dynamical models in the IRI plume continue to predict a weak and a short duration La Niña, as indicated by the Niño-3.4 index values less than -0.5°C. This prediction is also reflected in the latest North American Multi-Model Ensemble (NMME), which continues to predict slightly cooler SSTs and weak La Niña conditions. The forecast team leaned toward predicting an eventual onset of weak and short-lived La Niña conditions, based on the model guidance and current atmospheric anomalies. Weak La Niña conditions would be less likely to result in conventional winter impacts, though predictable signals could still influence the forecast guidance (e.g., CPC's seasonal outlooks).

... Read more at the NOAA's Diagnostic Discussion, CPC ENSO Update, and CPC's Official Probabilistic ENSO Forecast sites, all updated at the same time in the early-month.

** Note: IRI's Monthly Ouick Look updates twice per month and presents the latest update between the (I) early-month CPC official Probabilistic Forecast (shown in this section) and (II) mid-month IRI Model-Based Probabilistic Forecast (shown in the following two sections).

(The update of the CPC ENSO diagnostics discussion and forecast is scheduled for the second Thursday of each month.)




II) IRI Model-Based Probabilistic Forecast
(a purely objective ENSO probability forecast that uses as input the model predictions from IRI's ENSO Predictions Plume):

December 19, 2024  (updated mid-month)

As of mid-December 2024, ENSO-neutral conditions persist in the equatorial Pacific, and both oceanic and atmospheric indicators remain in an ENSO-neutral state. The IRI ENSO prediction plume forecasts slightly higher chances (59%) for ENSO-neutral conditions for Dec-Feb, 2025, with a continuation of ENSO-neutral conditions from Jan-Mar, 2025 to Jul-Sep, 2025. For Aug-Oct 2025, no specific ENSO category emerges as favored. In summary, ENSO-neutral conditions are expected to persist through the boreal winter, spring, and summer of 2025.


DISCUSSION:

According to the most recent official CPC ENSO Outlook (issued on December 12, 2024), the La Niña onset is forecasted in Nov-Jan 2024, with 59% chances; however, the objective IRI model-based ENSO outlook forecasts indicate the continuation of ENSO-neutral conditions for Dec-Feb, 2025. Thus, there is a notable difference between the probability numbers in the early-month CPC Outlook and mid-month IRI ENSO forecast. Going further forward, the CPC ENSO Outlook predicts a clear preference for La Niña during the winter of 2025, followed by a return to ENSO-neutral (61% chance in Mar-May) state during boreal spring of 2025. In contrast, the objective IRI ENSO forecasts show a continuation of ENSO-neutral conditions during the forecast period.

... Read more at the IRI Technical ENSO Update, IRI Model-Based Probabilistic ENSO Forecast, IRI ENSO Predictions Plume, and IRI Forecast Probability Distribution Based on the IRI ENSO Prediction Plume sites, all updated at the same time in the mid-month.

** Note: IRI's Monthly Ouick Look updates twice per month and presents the latest update between the (I) early-month CPC official Probabilistic Forecast (shown in this section) and (II) mid-month IRI Model-Based Probabilistic Forecast (shown in the following two sections).

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



III) IRI ENSO Predictions Plume
The following graph shows forecasts made by a set of dynamical and statistical models for SST in the Niño-3.4 region, for nine, overlapping, three-month periods.

December 19, 2024  (updated mid-month)

The IRI-Plume indicates ENSO-neutral conditions during Dec-Feb 2025. The multimodel mean of statistical models show ENSO-neutral conditions during the entire forecasts period; however, the multimodel mean of dynamical models show borderline La Niña conditions during boreal winter of 2025 (Dec-Feb, and Jan-Mar 2025), followed by a return to ENSO-neutral conditions.

... Read more here, where any specific model can be interactively examined, along with other detailed information.

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


IV) Frequently Used Figures
Click on the figures to access the web pages where these figures are described.

Nino 3.4 SST Anomaly Time Series SST Anomaly Map



Historically Speaking & More:

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

The spring predictability barrier: 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. This is a well-known challenge for forecaster and it can impact statistical models more than dynamical models.








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