The World Meteorological Organization (WMO) is studying the official declaration, in the coming weeks, of the end of the 2023-24 episode of the El Niño-Southern Oscillation (ENSO) climate phenomenon. The WMO's provisional assessment of March 3 indicated that El Niño conditions (above normal temperatures in the central Pacific Ocean) had weakened, although it warned that its impacts could continue for months (droughts and floods in various areas). points in America and Asia, mainly).
Pending an official statement from the WMO, both the United States Oceanic and Atmospheric Administration (NOAA) and the Australian Bureau of Meteorology have issued reports in recent days in which they consider that the 2023-24 El Niño episode can be considered finished.
NOAA forecasts "a transition to ENSO-neutral conditions by April-June 2024 (85% probability), with La Niña likely to develop by June-August 2024 (60% probability)."
The US Oceanic and Atmospheric Administration details that during March of this year "sea surface temperature (SST) anomalies continued to weaken in most of the equatorial Pacific Ocean, while SST anomalies were colder in the eastern end of the Pacific Ocean.
"Weekly SST index values in the other El Niño regions were between 0.9°C and 1.2°C. Below-average subsurface temperatures strengthened (average area index, reflecting the expansion of anomalies negative subsurface phenomena associated with an ascending Kelvin wave." On the other hand, NOAA details, "the low-level wind anomalies occurred over the western-central equatorial Pacific, while the upper-level wind anomalies occurred over the central-western equatorial Pacific. "Overall, the coupled ocean-atmosphere system reflected the continued weakening of El Niño," NOAA summarizes.
Current data indicates that there is "a transition to ENSO-neutral during spring 2024, with La Niña potentially developing in late summer 2024." In summary, a transition from El Niño to ENSO-neutral is likely to occur by April-June 2024 (85% probability), with La Niña likely to develop by June-August 2024 (60% probability.
The Australian Bureau of Meteorology indicates in a note published on April 16 that "the tropical Pacific Ocean has returned to ENSO-neutral" and that La Niña conditions may be recorded in the coming months. Despite remembering that short-term rain and temperature forecasts are not based solely on ENSO conditions, the Australian office indicates that in the current situation "it is likely that [in the coming months] temperatures will be above the average in most of the continent.
Most of Australia "has approximately the same probability of precipitation above or below" the average, indicates this specialized office, highlighting the difficulties in determining the immediate impact of the new ENSO situation. "Despite this, there is still a probability (between 10 and 30%) that rainfall will be significantly high or low," he adds without leaving any ambiguity. Additionally, in Australia "rainfall is likely to be below average in small areas of the southern mainland and parts of the north; however, in most of the north of the country rainfall is typically low at this time of year, with an average rainfall of less than 10 mm, indicates this office dependent on the Australian Government.
The effects of El Niño and La Niña vary depending on the intensity and geographical areas. Under current conditions, one of the data that could be elucidated is the possible relationship between El Niño conditions and the notable increase in temperature recorded across the planet in recent months. If a direct relationship existed, it could be expected that the disappearance of El Niño would mean a slowdown in global warming. However, some experts fear that even with an upcoming La Niña episode (cooling of the waters of the equatorial Pacific) temperatures will continue to set record highs.
La Niña events produce large-scale changes in atmospheric winds over the Pacific Ocean, including an increase in the intensity of the eastern trade winds (East-West) in the lower atmosphere over the eastern Pacific Ocean in South America, and from westerly winds in the upper atmosphere. Experts recall that during La Niña episodes, it is typical to observe drier conditions than normal over the central-equatorial part of the Pacific Ocean, due to a weakening of the jet stream between the months of December and February, and therefore strengthening monsoon systems in Australia, Southeast Asia, South America, Central America and Africa.
NOAA records indicate longest La Niña episodes in the periods 1954-1956, 1973-1976, 1998-2001, and 2020-2023. The recent event of greatest intensity occurred between 1973-1974, with a maximum in December 1973. Under La Niña conditions, in Central America it is quite likely to expect relatively wetter conditions than normal, mainly over the coastal areas of the Caribbean Sea. . In South America, drier and cooler than normal conditions prevail over Ecuador and Peru; dry and hot conditions in central Chile, as well as wetter conditions in Guyana and northeastern Brazil.
