Update on El Niño

According to data from the Australian Bureau of Meteorology, the El Niño phenomenon is continuing to weaken and transition to neutral conditions. Atmospheric and oceanic indicators of the El Niño-Southern Oscillation (ENSO) are likely to remain neutral at least until July 2024. Since December 2023, sea surface temperatures (SST) in the central Pacific have been steadily decreasing. Recent cloud and surface pressure patterns also indicate neutral conditions.

Figure 5.4 illustrates the variation in the Southern Oscillation Index (SOI) from April 2023 to April 2024. Over the past three months, the SOI values were at a low level in February 2024 (-12.6), followed by a rising trend, with March and April rebounding to neutral levels of SOI, indicating the El Niño phenomenon is declining and transitioning to neutral conditions.

Figure 5.4 Monthly time series of the SOI-BOM from April 2023 to April 2024 (Source:

http://www.bom.gov.au/climate/enso/soi/)

Another commonly used measure of El Niño events is called the Oceanic Niño Index (ONI). Figure 5.5 shows the locations of several NINO indices. An analysis of Table 5.1 reveals that during this four-month period, all three regions (NINO3, NINO3.4, and NINO4) have positive values, indicating sea surface temperatures above average levels. It is noteworthy that the positive values of the ONI index suggest the presence of El Niño conditions in the tropical Pacific region during this time. However, over the past four months, the ONI index has been gradually decreasing in all three regions, indicating that the El Niño phenomenon is weakening and transitioning to neutral conditions.

Figure 5.5 NINO Region Distribution Map（Source: 

https://www.ncdc.noaa.gov/teleconnections/enso/sst）

In March 2024, sea surface temperatures (SST) were nearly above the average level for the entire tropical Pacific. Between 10 degrees south and 10 degrees north latitude, sea temperature anomalies in most parts of the central and eastern Pacific were more than 0.8°C higher than the long-term (1961-1990) average. Compared to February 2024, the extent and magnitude of warm anomalies in the equatorial Pacific have decreased, reflecting the weakening of the El Niño phenomenon.

Figure 5.6 Monthly temperature anomalies for March 2024 (Source: http://www.bom.gov.au/climate/enso/wrap-up/#tabs=Sea-surface)

Table 5.1 ONI (°C) Anomaly Values from January 2024 to April 2024(Source: https://www.cpc.ncep.noaa.gov/data/indices/sstoi.indices)

According to the latest forecast from the NOAA Climate Prediction Center, the La Niña phenomenon is expected to develop during July to September 2024 and then persist into the Northern Hemisphere winter. La Niña typically follows strong El Niño events, providing additional confidence in the pattern guidance favorable to La Niña. Overall, there may be a transition from El Niño to ENSO neutral conditions next month. La Niña is likely to occur in either June to August (49% chance) or July to September (69% chance).

Global Impact on temperature

2024 is proving to be a typical El Niño year. Since the second half of 2023, sea temperatures in the central and eastern equatorial Pacific have been consistently rising, meeting the criteria for an El Niño event. According to data from the National Oceanic and Atmospheric Administration (NOAA), sea surface temperatures in the central equatorial Pacific reached anomalies of over 1.5°C from January to April 2024, the highest level since the 1997-1998 El Niño event. The anomalous distribution of sea temperatures affects atmospheric circulation and precipitation patterns, leading to abnormal weather conditions globally.

Global impacts on precipitation

El Niño's impact on global precipitation from January to April influencex agricultural productivity, water resources, and disaster preparedness. Monitoring these patterns is crucial for mitigating adverse effects and planning appropriate responses. El Niño typically brings increased rainfall to the western and southeastern U.S., central and southern South America, and eastern Africa from January to April. Conversely, it causes drier conditions in Southeast Asia, eastern Australia, northern South America, and southern Africa. These changes can lead to flooding in wetter regions and droughts in drier ones, significantly impacting agriculture and water resources.

On April 27, 2024, a powerful storm bringing strong winds and heavy rains began sweeping through the southernmost state of Rio Grande do Sul in Brazil. In some areas, rainfall exceeded 300 millimeters in less than a week, causing rivers to overflow and resulting in widespread, destructive flooding (Figure 5.7).

Figure 5.7 Brazil is experiencing flooding

From January to April 2024, the combination of intense heat and below-average rainfall has resulted in drought conditions in much of the Philippines (Figure 5.8). According to data from the Climate Hazards Center at the University of California, Santa Barbara, rainfall in most parts of the country during the first four months of 2024 has been only 45% to 75% of the expected amount.

Figure 5.8 Southeast Asia is experiencing severe drought