MELBOURNE, Australia – The 2020–21 La Niña is likely to have peaked in terms of sea surface temperatures in the Pacific Ocean, reports the Bureau of Meteorology (BOM) of the Australian Government in its latest update. However, impacts associated with La Niña, such as above-average rainfall, are expected to persist across eastern and northern Australia through the summer months, with climate outlooks indicating above-average rainfall is particularly likely across the eastern third of the country.
Over the past fortnight here has been little change in sea surface temperatures across the central Pacific Ocean, which have been close to the La Niña threshold of 0.8 °C below average since early December. However, the Southern Oscillation Index has risen sharply and is currently at +18.8, well above the La Niña threshold of +7.
Model outlooks indicate the strength of La Niña is likely to ease in the coming weeks with a likely return to neutral conditions during the late southern summer or early autumn.
The Southern Annular Mode (SAM) continues to be strongly positive. While positive SAM often occurs during La Niña, the current event is also being driven by an exceptionally strong polar vortex over Antarctica. Positive SAM values are expected until late January 2021. A positive SAM at this time of year typically increases the chance of rainfall in eastern Australia.
The Madden–Julian Oscillation (MJO) is located over the Indian Ocean. It is relatively weak, although most models indicate it may strengthen marginally in the coming week. The MJO is not expected to significantly influence tropical weather in the Australian region in the coming fortnight.
Climate change is also influencing the Australian climate. Rainfall across northern Australia during its wet season (October–April) has increased since the late 1990s with a greater proportion of high intensity short duration rainfall events.
