El Niño conditions have prevailed in the equatorial Pacific in recent months, and sea surface temperatures here are still clearly above average. However, the peak now seems to have passed and there are increasing signs that the ENSO swing is tipping again.
The signs are pointing to a slowdown
The cyclical change between El Niño and its cold sister La Niña (ENSO – El Niño Southern Oscillation) is one of the most well-known climate phenomena on Earth. The temperature conditions at the sea surface in the equatorial Pacific not only have a major impact on local weather dynamics, but also affect a number of other regions of the world via teleconnection. But there are natural variations. In Australia, the period from August to October was dry as expected (in fact, the driest since records began), but the influence of El Niño then waned and it became wetter. The Amazon basin has been suffering from an exceptional drought for months, and temperatures have also recently been well above average. In East Africa, it has recently been wetter than usual, which is in line with expectations for El Niño.
Fig. 1: Course of the sea surface temperature anomaly in the equatorial Pacific since February 2023. End of La Niña, change to El Niño; Source: NOAA
El Niño reached its peak between November and early January, with the warm surface water reaching its greatest extent. This is also normal – hence the name (the child or the Christ child). In the first few weeks of the year, however, the water in the eastern Pacific began to cool, and the trend has recently intensified. There is now also a negative trend in the central Pacific.
Fig. 2: Deviation of sea surface temperature in the Pacific from the norm in the past month; Source: NOAA
The ENSO swing tilts again
La Niña was able to hold its own for almost three years in a row until the beginning of 2023, after which there was a switch to a strong El Niño. According to the latest forecasts, however, we can expect another reversal in the coming months. El Niño should therefore continue to weaken in the coming weeks, but its influence on global weather patterns will continue (the atmosphere reacts with a time lag).
Fig. 3: Current ENSO forecasts from the various computer models for the coming months; Source: IRI
According to some models, a neutral state will already be reached between March and May, while more conservative approaches see this occurring between April and June. In any case, the days of this El Niño event are probably numbered. Another change to La Niña seems likely for the second half of the year.
Fig. 4: Probabilities for the further ENSO development in the coming months; Source: IRI
The interactions between the ocean and the atmosphere are very complex, and there are no simple and general answers. As was the case for most of last year, the average global sea surface temperature between 60 degrees north and 60 degrees south is currently at record levels, and by a wide margin. The degree of deviation is unprecedented in the era of satellite observations.
Fig. 5: Development of the mean global sea surface temperature for the years 1981-2024; Source: University of Maine
With the cooling of the equatorial Pacific and thus of a very large ocean area, this should weaken somewhat. El Niño and La Niña are also known to have an impact on the Atlantic hurricane season. The latter improves the atmospheric conditions for hurricane formation in the Atlantic basin (including low wind shear). In this case, the timing would be poor. Above-average water temperatures meet improving atmospheric conditions in the fall. It will be interesting to see how this circumstance is reflected in the initial forecasts of the various institutes for the coming hurricane season.
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