ENSO Conditions and Coral Bleaching

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):

April 10, 2025 (updated early-month)

Alert Status: Final La Niña Advisory
(definitions)

ENSO-neutral is favored during the Northern Hemisphere summer, with a greater than 50% chance through August-October 2025

DIAGNOSTIC DISCUSSION:

In March 2025, ENSO-neutral conditions returned, with below-average sea surface temperatures (SSTs) weakening in the central and east-central equatorial Pacific Ocean. The westernmost Niño index values were near zero, while positive index values persisted in the easternmost Niño-3 and Niño-1+2 regions. Below-average subsurface temperatures weakened, but negative anomalies continued in the central equatorial Pacific, extending to 250m depth. A shallow layer of above-average subsurface temperatures continued in the far eastern equatorial Pacific.

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

Last month, the IRI and North American multi-model ansemble indicate ENSO-neutral would continue through the summer. The forecast team also favors ENSO-neutral, with chances well over 50% through summer 2025. Because of reduced forecast accuracy in the spring, the uncertainty increases at longer time horizons, with a 43% chance of ENSO-neutral and a 38% chance of La Niña during November 2025 - January 2026 (chances of El Niño are under 20%).

... 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):

April 21, 2025 (updated mid-month)

During the forecast period, neither El Niño nor La Niña shows a strong preference, with the probabilities for both phases gradually increasing and then stabilizing in the upper 20% range.

As of mid-April 2025, the equatorial Pacific is in an ENSO-neutral state. This shift is marked by sea surface temperatures in the Niño 3.4 region that are now closer to average, with anomalies at 0.10°C for Mar, 2025. The IRI ENSO plume forecast indicates a high probability (96%) of ENSO-neutral conditions for April to June 2025. These neutral conditions are expected to continue through August to October 2025, with probabilities staying above 50%. For later forecast seasons, ENSO-neutral conditions remain the most likely outcome, though probabilities decrease to the 40% range.

... 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.

April 21, 2025 (updated mid-month)

The IRI ENSO prediction plume indicates a high likelihood of ENSO-neutral conditions during Apr–Jun 2025. The multimodel mean of statistical and dynamical models shows ENSO-neutral conditions remaining above 50% probability through August–October 2025, then decreasing to the 40% range for the remainder of the forecast period. These forecasts show no particular preference for either El Niño or La Niña, both of which remain in the 20% probability range throughout the forecast period.

... 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.)

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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