Chance of above average rainfall across much of northern and eastern Australia continues during Summer

Australian Bureau of Meteorology (BOM), 21 December 2021:

The ENSO Outlook is at LA NIÑA.

Key atmospheric and oceanic indicators of the El Niño–Southern Oscillation (ENSO) show an established La Niña. Tropical Pacific sea surface temperatures (SSTs) are at La Niña thresholds, with models indicating further cooling is likely in January. Atmospheric indicators including the Southern Oscillation Index (SOI), trade wind strength, and equatorial cloudiness have responded to this oceanic cooling and are typical of La Niña conditions.

The current model outlooks suggest this La Niña will persist until the late southern hemisphere summer or early autumn 2022. All but one of the models surveyed by the Bureau indicate SSTs will meet La Niña thresholds until at least February 2022.

Bureau climatologists will continue to closely monitor conditions in the tropical Pacific as well as model outlooks for further changes to this La Niña event.

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La Niña continues as Indian Ocean Dipole returns to neutral

La Niña conditions continue in the tropical Pacific. Climate models suggest this La Niña will persist until the late southern hemisphere summer or early autumn 2022. La Niña events increase the chance of above average rainfall across much of northern and eastern Australia during summer.

Most indicators of the El Niño–Southern Oscillation (ENSO) show clear La Niña patterns. Sea surface temperatures (SSTs) in the tropical Pacific remain at, or exceed, La Niña thresholds, with cooler water beneath the surface to support further cooling. In the atmosphere, cloud, wind, and pressure patterns are typical of La Niña, indicating the atmosphere is responding to the ocean changes below. These atmospheric changes also reinforce the changes observed in the ocean. This feedback process is known as 'coupling' and allows La Niña conditions to be sustained for an extended period.

The Indian Ocean Dipole (IOD) is neutral. Cloud and wind patterns, as well as SSTs, have now eased back from a negative IOD-like state and become more clearly neutral. Climate models predict the IOD will remain neutral for the coming months, consistent with its typical seasonal cycle. A neutral IOD has little influence on Australian climate.

The Madden–Julian Oscillation (MJO) remains in the western Pacific. The MJO is forecast to progress eastwards across the western Pacific over the coming fortnight, which would typically increase cloudiness and rainfall across northern Australia and the western Pacific. It also increases the chances that the monsoon will develop in the Australian region by encouraging westerly winds over the area. However, as these westerly winds get further into the western Pacific, they could act to temporarily weaken the La Niña.

The Southern Annular Mode (SAM) continues to be positive. It is forecast to remain at positive levels until the end of the year before returning to neutral. A positive SAM during summer typically brings wetter weather to eastern parts of Australia, but drier than average conditions for western Tasmania.

Climate change continues to influence Australian and global climate. Australia's climate has warmed by around 1.44°C for the 1910–2019 period. Rainfall across northern Australia during its wet season (October–April) has increased since the late 1990s. In recent decades there has been a trend towards a greater proportion of rainfall from high-intensity short-duration rainfall events, especially across northern Australia.