According to the Australian Government Bureau of Meteorology, The Pacific Ocean is currently ENSO- neutral (neither La Niña nor El Niño), with anomalous warmth in both the east and west of the basin. While oceanic ENSO indicators have continued to warm and are forecast to reach El Niño thresholds during winter, there has been little to no shift towards El Niño in atmospheric ENSO indicators. As a result, the ENSO Outlook remains at El Niño WATCH. This means there is approximately a 50% chance of El Niño developing in 2023 [1].

Figure 5.7 depicts the standard Southern Oscillation Index (SOI) behavior from April 2022 to April 2023. The SOI has been positive and high (greater than +7) in January and February 2023. However, there has been a significant weakening trend, with the SOI declining to -2 and +0.3 in March and April 2023, respectively. This indicates that the La Niña event has concluded.

The Oceanic Niño Index (ONI) is another widely-used measure of El Niño. Figure 5.8 displays several ONIs and their respective locations. The data analysis in Table 5.1 shows a transition from cooler conditions towards a warming trend in the central and eastern equatorial Pacific Ocean during the first four months of 2023. The NINO3, NINO4, and NINO3.4 indices consistently demonstrate this shift, with sea surface temperatures progressively approaching or surpassing average values.

Sea surface temperature (SSTs) (Figure 5.9) for April 2023 were warmer than average over the eastern, southern, and far west of the tropical Pacific Ocean. Warm anomalies up to 2 °C warmer than average were present over these regions, increasing to more than 4 °C warmer than average off parts of the South American coast.

In conclusion, the recent La Niña event in winter has concluded, and the tropical Pacific is currently experiencing a warming phase. However, the atmospheric response to this warming trend remains minimal. It remains to be seen whether an El Niño event will occur in the future.

Figure 5.7 Monthly SOI-BOM time series from April 2022 to April 2023

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

Figure 5.8 Map of NINO Region

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

Figure 5.9 Monthly temperature anomalies for April 2023

(Source: http://www.bom.gov.au/climate/enso/index.shtml#tabs=Pacific-Ocean)

Table 5.1 Anomalies of ONIs (°C), January to April 2023

(Source: https://www.cpc.ncep.noaa.gov/data/indices/sstoi.indices)

Main Sources:

[1] http://www.bom.gov.au/climate/enso/index.shtml#tabs=Overview