The El Niño phenomenon is now over in 2024

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Pacific seawater temperature anomalies with cold/warm anomalies in blue/red tones, with a strong El Niño signal shown in the image. Climate Reanalyzer.
Francisco Martin León Francisco Martin León Weathered Spain 5 minutes

Phenomenon El Nino has gained momentum in recent months. Ocean surface temperatures (SSTs) were above average throughout the equatorial Pacific (Fig. 1) and increased in the central and eastern central Pacific during November.

However, the growth of SST anomalies slowed in early December, with the last weekly El Niño index values ​​of +1.4 °C in Niño-4, +1.9 °C in Niño-3, 4, +2.0 °C in Niño -3 and +1.3°C in Niño-1+2 (Fig. 2).

Area-averaged surface temperature anomalies increased significantly during November (Fig. 3), reflecting the strengthening above-average surface temperatures in the central and eastern Pacific associated with the sinking of the oceanic Kelvin wave (Fig. 4).

Low-level wind anomalies were westerly in the central and eastern Pacific, while upper-level wind anomalies were easterly in the Pacific. Convection and precipitation remained enhanced around the international datum and suppressed near Indonesia (Fig. 5).

The equatorial and station Southern Oscillation Index (SOI) were negative. All in all, the coupled ocean-atmosphere system reflects a growing El Niño.

El Niño is expected to continue throughout the Northern Hemisphere winter, with a transition to ENSO-neutral in April-June 2024 (60% probability).

This is indicated by the latest IRI forecasts El Nino it will continue until the boreal winter of 2023-24 (Fig. 6), after which it will begin to weaken.

Based on the latest predictions there is a 54% chance of a “historically strong” El Niño (≥ 2.0 °C to Niño-3.4) during the November-January season. An event of this intensity could be in the top 5 events since 1950.

How long should it take? El Nino?

While a stronger El Niño event increases the likelihood of El Niño-related climate anomalies, it does not necessarily equate to locally strong impacts (see the CPC Seasonal Outlook for temperature and precipitation probabilities).

In summary, El Niño is expected to continue throughout the Northern Hemisphere winter, with a transition to ENSO-neutral most likely in April–June 2024 (60% probability; (Fig. 7)).

This means that here in Italy the indirect effect of El Niño will continue to be felt until next summer, with long hot periods, due to the dynamics already explained in this item.

Will there be severe heat waves?

All this thanks to the so-called “tropospheric rivers” (meteorologists call it that), that is, the flow of air masses that expand from the warm surface of the ocean along the entire tropospheric column.

The presence of strong positive thermal anomalies on the surface of the Northeast Pacific with values ​​of approximately +2.5°C +3.0°C compared to the traditional climatological average transfers a large amount of latent heat to the overlying air masses which gradually rise to the upper troposphere.

“Tropospheric rivers” rising from the very warm surface waters of the eastern tropical Pacific, especially from the area around Hawaii, contribute to the strengthening and even stronger strengthening of the anticyclonic ridges associated with “Hadley Cell”.

After reaching a certain height, almost at the border of the stratosphere, these very hot air masses, but also rich in water vapor, across subtropical latitudes they tend to descend (“atmospheric depressions”) and feed an anticyclonic band, known as a “Hadley cell”, which usually persists in the region.

The latter, supported by this “tropospheric river” of particularly hot air drawn in by the warm surface waters of the eastern Pacific, much warmer than normal, it tends to elongate along the meridians, usually with two narrower-than-normal ascending branches that stretch across the American West Coast and the eastern Atlantic (in front of western Europe), also carrying intense heat waves to these areas.



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