From BOM
The 30-day Southern Oscillation Index (SOI) has seen recent values fall to El Niño levels, but in the longer-term, values remain neutral. The SOI for the 30 days ending 9 June is −9.6, with the 90-day average −6.2.
Sustained negative values of the SOI below −7 typically indicate El Niño while sustained positive values above +7 typically indicate La Niña. Values between +7 and −7 generally indicate neutral conditions.
The tropical Pacific Ocean and atmosphere remain near El Niño thresholds, meaning the ENSO Outlook remains at El Niño WATCH. Climate models suggest a gradual shift away from El Niño levels over the coming months. Indian Ocean temperature forecasts, on the other hand, show a positive Indian Ocean Dipole (IOD) through the southern winter, which is likely to be the dominant climate driver for Australia.
A fortnight ago, a pulse of the Madden–Julian Oscillation (MJO) weakened trade winds, which led to some renewed warming at the surface of the tropical Pacific Ocean. However, this MJO pulse has passed, returning trade winds to normal levels. With little warmth in the ocean sub-surface, most climate models suggest the tropical Pacific will cool, shifting away from El Niño thresholds, during winter.
In the Indian Ocean, waters off Sumatra have cooled over the past fortnight, with the IOD index now exceeding positive thresholds for three weeks. All but one of the climate models suggest positive IOD values will persist through winter and into spring. To be considered a positive IOD event, positive thresholds need to be maintained for at least two months.