According to data from the Australian Bureau of Meteorology, the El Niño phenomenon has remained neutral during this monitoring period (April to July) and is transitioning towards La Niña. Over the past four months, sea surface temperatures in the central and eastern equatorial Pacific have continued to decrease. Atmospheric patterns, including cloud cover, winds, and trade winds, are currently indicating an ENSO-neutral state, with La Niña possibly beginning to develop in the fall of this year.

Figure 5.4 shows the changes in the standardized Southern Oscillation Index (SOI) from July 2023 to July 2024. During April, May, and June, the SOI values remained at neutral levels. Over the past three months, the SOI values have steadily declined and dropped below -7 in July (-9.5).

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

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

Another commonly used indicator for measuring the El Niño phenomenon is known as the Oceanic Niño Index (ONI). Figure 5.5 displays several ONI values and their locations. An analysis of Table 5.1 reveals that in May, the ONI anomalies for all three regions (NINO3, NINO3.4, and NINO4) showed a significant decrease compared to April. The values for the NINO3.4 and NINO4 regions continued to decline throughout the quarter, indicating a persistent decrease in sea surface temperatures. This suggests that El Niño conditions remain neutral and may potentially transition towards La Niña.

Figure 5.5 NINO Region Distribution Map（Source: 

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

In July 2024, sea surface temperatures (SST) were mostly at or slightly above average. However, temperatures in much of the western tropical Pacific were 1.2°C above average, and 2°C above average in the far eastern regions. In parts of the equatorial Pacific east of 140°W and along the South American coast, temperatures were 2°C below average. Based on the latest ocean observations and predictions from various climate models around the world, the cooling trend in the central and eastern equatorial Pacific is expected to continue in the coming months.

Figure 5.6 Monthly temperature anomalies for July 2024 (Source:

http://www.bom.gov.au/climate/enso/wrap-up/#tabs=Sea-surface)

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

According to the latest forecast from the NOAA Climate Prediction Center, ENSO-neutral conditions are expected to persist over the next few months, with La Niña likely to emerge between September and November (with a 66% probability) and continue through the Northern Hemisphere winter of 2024-25 (with a 74% probability during the November to January period).

Global Impact

Although sea surface temperatures in the equatorial Pacific continued to decline this quarter, global sea temperatures from April 2023 to June 2024 were the highest on record for each month. In July 2024, global sea temperatures were the second hottest July on record.

The World Meteorological Organization (WMO) has issued a recent bulletin indicating that La Niña is likely to reemerge later this year. 

La Niña not only impacts the climate in the Pacific region but also has widespread effects on global climate. Under La Niña conditions, increased rainfall in Indonesia and other parts of the Maritime Continent could lead to flooding, while the risk of drought will significantly increase in the central and eastern Pacific as well as western South America.