MELBOURNE, Australia – The El Niño–Southern Oscillation (ENSO) remains neutral, with sea surface temperatures (SSTs) in the central equatorial Pacific Ocean at ENSO-neutral levels, reports the Bureau of Meteorology of the Australian Government in its latest update. Atmospheric indices, such as those related to patterns of surface pressure, cloud and trade winds, are broadly consistent with an ENSO-neutral state.
While some have displayed La Niña-like signals over recent months, a consistent and sustained shift in the atmosphere has not been observed. Ocean temperatures in the central equatorial Pacific have started to warm in recent weeks, away from the La Niña threshold, although they are still cooler than the historical average.
The Bureau’s model suggests SSTs are likely to remain within the ENSO-neutral thresholds (−0.8 °C to +0.8 °C) throughout the forecast period to February 2025. Of the 6 other climate models surveyed, 2 models suggest SSTs in the tropical Pacific are likely to exceed the La Niña threshold (below −0.8 °C) throughout December to February, which is sufficient time to be classified as a La Niña event, though this would be considered a very short-lived event compared to the historical record. All models forecast neutral ENSO values by March.
The Indian Ocean Dipole (IOD) index has been below the negative IOD threshold (−0.40 °C) since mid-October. If the IOD index remains below the threshold for another week, it would indicate a negative IOD event is underway. However, all but one of the surveyed climate models indicate that the IOD index is expected to return to neutral levels in December, in line with the typical IOD event lifecycle.
Global SSTs remain at near record levels as at 24 November, with temperatures since July falling just short of the record temperatures observed during 2023, yet above all other years since observations began in 1854. The sustained nature of this significant global ocean heat suggests that climate indicators such as ENSO and IOD may not behave or evolve as they have in the past.
The Southern Annular Mode (SAM) index is neutral as at 23 November, having been positive for most of November. It is forecast to become positive again in the coming fortnight. SAM is also forecast to have a greater than usual chance of being in the positive phase during December.
A moderate to strong pulse of the Madden–Julian Oscillation (MJO) is currently located in the Indian Ocean (as at 24 November). Most models indicate the MJO will shift eastwards over the coming fortnight and weaken in early December as it moves across the Maritime Continent.
ENSO, IOD, MJO and SAM are broad indicators of the expected climate and are just some of many factors in a complex system. The long-range forecast provides better guidance on local rainfall and temperature patterns.
