Friday 24 June 2022

La Niña remains active, but expected to weaken

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MELBOURNE, Australia – The 2021–22 La Niña event continues, despite some weakening over recent weeks. Climate outlooks continue to indicate a return to neutral El Niño–Southern Oscillation (ENSO)—neither La Niña nor El Niño—during the late southern hemisphere autumn or in early winter.

According to the latest update from the Bureau of Meteorology of the Australian Government, even as La Niña weakens, it will continue to influence global weather and climate. La Niña events increase the chances of above average rainfall across large parts of eastern Australia during autumn.

Atmospheric and most oceanic indicators of ENSO persist at La Niña levels. Sea surface temperatures remain cooler than average along the equator. Compared to two weeks ago, surface waters have cooled slightly in the eastern half of the equatorial Pacific. Trade winds remain stronger than average in the western Pacific. Other atmospheric indicators also remain at La Niña levels, with decreased cloudiness persisting along the Date Line and a positive Southern Oscillation Index (SOI).

The Madden–Julian Oscillation (MJO) has been weak or indiscernible for the past fortnight. Climate models indicate the MJO is likely to remain weak, having little influence on tropical weather and climate in the coming fortnight.

The Southern Annular Mode (SAM) index is positive, but is expected to be neutral to weakly positive over the coming two weeks. During autumn SAM typically has a weaker influence on Australian rainfall.

The Indian Ocean Dipole (IOD) is neutral. It typically has little influence on global climate patterns from December to April due to the influence of the monsoon. Outlooks for the IOD indicate potential for a negative IOD to develop in the coming months, however, at this time of year model outlooks have low accuracy for outlooks beyond autumn.

Climate change continues to influence Australian and global climate. Australia’s climate has warmed by around 1.47 °C for the 1910–2020 period. Southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades, while rainfall across northern Australia during its wet season (October–April) has increased. 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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