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):

July 10, 2025 (updated early-month)

Alert Status: Not Active
(definitions)

ENSO-neutral is most likely through the late Northern Hemisphere summer 2025 (56% chance in August-October). Thereafter, chances of La Niña conditions increase into the fall and winter 2025-26, but remain comparable to ENSO-neutral.

DIAGNOSTIC DISCUSSION:

During June 2025, ENSO-neutral continued, with near-average sea surface temperatures (SSTs) prevailing across most of the equatorial Pacific Ocean. The latest weekly Niño index values ranged from 0.0°C to +0.4°C. Subsurface temperature anomalies were weakly positive and nearly unchanged from last month, with mostly above-average temperatures established along the thermocline.

Over the east-central and eastern equatorial Pacific Ocean, low-level wind anomalies were easterly and upper-level wind anomalies were westerly. Convection remained enhanced over Indonesia. Collectively, the coupled ocean-atmosphere system in the tropical Pacific reflected ENSO-neutral.

Last month, the IRI predictions indicate ENSO-neutral is most likely through the Northern Hemisphere winter 2025-26. In contrast, the North American Multi-Model Ensemble favors the onset of La Niña conditions during the Northern Hemisphere fall, though lasting a shorter duration than NOAA's requirement of five consecutive overlapping 3-month seasons. While the subsurface equatorial Pacific remains above average, easterly trade winds are predicted to strengthen in the coming month, which could portend cooler conditions. In summary, ENSO-neutral is most likely through the late Northern Hemisphere summer 2025 (56% chance in August-October).

... 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):

July 18, 2025 (updated mid-month)

The neutral conditions are expected to persist through the end of the forecast period.

As of mid-July 2025, the equatorial Pacific remains in an ENSO-neutral state, with sea surface temperatures in the Niño 3.4 region close to average. The IRI ENSO plume forecast indicates a high probability (75%) of ENSO-neutral conditions for Jul–Sep 2025. These neutral conditions are expected to persist through the end of the forecast period. For later seasons (Oct–Dec and Nov–Jan), the probabilities for ENSO-neutral decrease slightly to 49% and 49%, respectively, but remain higher than those for either La Niña or El Niño. Looking ahead to the 2025/2026 period, ENSO-neutral once again becomes the dominant category, with gradually increasing probabilities.

... 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.

July 18, 2025 (updated mid-month)

The IRI ENSO prediction plume indicates a high likelihood of ENSO-neutral conditions during Jul–Sep 2025 (75% chance). The multimodel mean of statistical and dynamical models shows ENSO-neutral conditions remain dominant throughout the forecast period, with a slight decrease in probability during Oct–Dec and Nov–Dec, followed by an increase from Dec–Feb through the end of the forecast period. 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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