MELBOURNE, Australia – A La Niña is underway in the tropical Pacific, reports the Bureau of Meteorology (BOM) of the Australian Government in its latest release. All surveyed international climate models indicate this La Niña will persist through the southern hemisphere summer 2020–21.
Most models suggest the La Niña will strengthen, peaking in December. Around half the models anticipate a strong event, meaning there is a possibility it could reach similar strength to the 2010–12 event. However, models forecast this event will be shorter, possibly ending in the first quarter of 2021. The strength of La Niña impacts on Australia are often related to the strength of the event.
Central and eastern tropical Pacific Ocean sea surface temperatures remain around La Niña thresholds (0.8 °C below average) and atmospheric indicators, including the Southern Oscillation Index (SOI), trade winds and cloud, are also at La Niña levels.
The ENSO’s negative phase typically increases the chance of above average rainfall across much of Australia during spring. Above average summer rainfall is also typical across eastern Australia. Current climate outlooks indicate November 2020 to January 2021 will be wetter than average for much of the country.
In the Indian Ocean, there has been significant warming of sea surface temperatures in the west of the Basin over the past fortnight. Models have reduced the likelihood of a negative IOD event in 2020, noting that the IOD typically breaks down in late spring or early summer.
The Southern Annular Mode (SAM) is expected to be positive for the remainder of October. La Niña tends to favour positive SAM during spring and summer, further enhancing the wet signal in the east.
The Madden–Julian Oscillation (MJO) is in the Maritime Continent and is expected to increase in strength as it moves into the Western Pacific Ocean.
Climate change is also influencing the Australian climate. Australia’s climate has warmed by around 1.4 °C since 1910, while southern Australia has seen a 10–20% reduction in cool season (April–October) rainfall in recent decades.