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):

May 8, 2025 (updated early-month)

Alert Status: Not Active
(definitions)

ENSO-neutral is favored through the Northern Hemisphere summer 2025 (74% chance during June-August), with chances exceeding 50% through August-October 2025

DIAGNOSTIC DISCUSSION:

In April 2025, ENSO-neutral continued, with near-average sea surface temperatures (SSTs) covering most of the equatorial Pacific Ocean. All of the latest weekly Niño index values were near zero, ranging from -0.2°C to +0.1°C. Subsurface temperatures were mostly near average in the central and eastern Pacific Ocean, with above-average subsurface temperatures remaining at depth in the western Pacific.

For the month, low-level and upper-level winds were near average across the equatorial Pacific. Convection remained suppressed near and west of the Date Line and was enhanced near Indonesia. Collectively, the coupled ocean-atmosphere system was ENSO-neutral.

Last month, the IRI and North American multi-model ansemble anticipate ENSO-neutral to continue through the Northern Hemisphere summer and early autumn 2025. The forecast team also favors ENSO-neutral, especially through the summer, with chances nearing 50% during the autumn. The uncertainty increases at longer time horizons, with a 46% chance of ENSO-neutral and a 41% chance of La Niña during November 2025 - January 2026 (chances of El Niño are under 15%).

... 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):

May 19, 2025 (updated mid-month)

During the forecast period, neither El Niño nor La Niña shows a strong preference, though La Niña have slightly higher chances as compared to El Niño.

As of mid-May 2025, the equatorial Pacific is in an ENSO-neutral state, with sea surface temperatures in the Niño 3.4 region that are close to average (-0.10°C for April 2025). The IRI ENSO plume forecast indicates a high probability (92%) of ENSO-neutral conditions for May to July 2025. These neutral conditions are expected to continue through August to October 2025, with probabilities remaining above 50%. For later forecast seasons (until Jan–Mar 2026), 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.

May 19, 2025 (updated mid-month)

The IRI ENSO prediction plume indicates a high likelihood of ENSO-neutral conditions during May–Jul 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 through Jan–Mar 2026. These forecasts show a slightly preference for La Niña as compared to El Niño.

... 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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