A La Niña Watch has been issued as climate scientists see evidence for a coming flip from El Niño to La Niña. We have been in a strong El Niño, but ocean water temperatures in the Pacific have started to change suggesting a change to this global circulation pattern is coming. 

A La Niña Watch is issued when conditions are favorable for the development of La Niña conditions within the next six months. At the same time an El Niño Advisory remains in effect because El Niño conditions are observed and expected to continue in the short term. 

Below is part of the discussion from NOAA's Climate Prediction Center on this pattern change: 

A transition from El Niño to ENSO-neutral is likely by April-June 2024 (79% chance), with increasing odds of La Niña developing in June-August 2024 (55% chance).

During January 2024, above-average sea surface temperatures (SST) continued across most of the equatorial Pacific Ocean [Fig. 1]. SST anomalies weakened slightly in the eastern and east-central Pacific, as indicated by the weekly Niño index values [Fig. 2]. However, changes were more pronounced below the surface of the equatorial Pacific Ocean, with area-averaged subsurface temperature anomalies returning to near zero [Fig. 3]. Although above-average temperatures persisted in the upper 100 meters of the equatorial Pacific, below-average temperatures were widespread at greater depths [Fig. 4]. Atmospheric anomalies across the tropical Pacific also weakened during January. Low-level winds were near average over the equatorial Pacific, while upper-level wind anomalies were easterly over the east-central Pacific. Convection remained slightly enhanced near the Date Line and was close to average around Indonesia [Fig. 5]. Collectively, the coupled ocean-atmosphere system reflected a weakening El Niño.

The most recent IRI plume indicates a transition to ENSO-neutral during spring 2024, with La Niña potentially developing during summer 2024 [Fig. 6]. Even though forecasts made through the spring season tend to be less reliable, there is a historical tendency for La Niña to follow strong El Niño events. The forecast team is in agreement with the latest model guidance, with some uncertainty around the timing of transitions to ENSO-neutral and, following that, La Niña. Even as the current El Niño weakens, impacts on the United States could persist through April 2024. 

The Climate Prediction Center defines. . .

"El Niño conditions" as existing when:

    • A one-month positive sea surface temperature anomaly of 0.5° C or greater is observed in the Niño-3.4 region of the equatorial Pacific Ocean (5° N - 5° S, 120° W - 170° W) and an expectation that the 3-month Oceanic Niño Index (ONI) threshold will be met, AND
    • An atmospheric response typically associated with El Niño is observed over the equatorial Pacific Ocean (see The ENSO Cycle).

"La Niña conditions" as existing when:

    • A one-month negative sea surface temperature anomaly of -0.5° C or less is observed in the Niño-3.4 region of the equatorial Pacific Ocean (5° N - 5° S, 120° W - 170° W) and an expectation that the 3-month Oceanic Niño Index (ONI) threshold will be met , AND
    • An atmospheric response typically associated with La Niña is observed over the equatorial Pacific Ocean (see The ENSO Cycle).

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