Tuesday 30 May 2023

La Niña is firmly established in tropical Pacific and will persist until late summer

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MELBOURNE, Australia – La Niña is firmly established in the tropical Pacific reports the Bureau of Meteorology of the Australian Government in its latest update. 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 El Niño–Southern Oscillation (ENSO) indicators show clear La Niña patterns. Sea surface temperatures in the tropical Pacific have cooled to La Niña thresholds, with climate model outlooks expecting them to cool further.

In the atmosphere, cloud and wind patterns are typical of La Niña, indicating the atmosphere is responding to the changes in ocean temperatures. This feedback process is known as “coupling”, and it means La Niña conditions are now expected to be locked in until at least the end of summer.

The negative Indian Ocean Dipole (IOD) is near its end, with IOD index values in the neutral range. However, some signs of the negative IOD persist with increased cloud over the eastern Indian Ocean and strengthened westerly winds. Climate models predict the IOD will remain neutral for the coming months, consistent with its typical seasonal cycle.

The Madden–Julian Oscillation (MJO) has recently entered the western Pacific and strengthened. The MJO is forecast to progress eastwards across the western Pacific over the coming fortnight, which increases the likelihood of above average cloudiness and rainfall across northern Australia and the western Pacific. It also increases the chance that the monsoon will develop in the Australian region in the next week or two—a little earlier than normal.

The Southern Annular Mode (SAM) continues to be positive and is forecast to remain positive levels to at least to the end of the year. 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.

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