Source: Bureau of Meteorology — ENSO Outlook [updated every 2 weeks]

La Niña underway in the tropical Pacific


The Bureau’s ENSO Outlook has moved to LA NIÑA, indicating La Niña is established in the tropical Pacific. All surveyed international climate models indicate this La Niña will persist until at least January 2021.

While models agree La Niña will continue well into summer 2020–21, around half the models predict a strong event, while 3 of 8 models suggest moderate strength. Overall, models do not currently anticipate this event will be as strong as the La Niña of 2010–12, which was one of the four strongest La Niñas on record. 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 exceed 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.

In the Indian Ocean, the latest values of the Indian Ocean Dipole (IOD) index have again gone into negative dipole territory. Five of the 6 surveyed models indicate the IOD will be negative for October, and three models continue negative IOD values into November.

Both La Niña and negative IOD typically increase the chance of above average rainfall across much of Australia during spring. Above average summer rainfall is also typical across eastern Australia during La Niña. Current climate outlooks indicate the remainder of 2020 will be wetter than average across the eastern two thirds of Australia.

The Southern Annular Mode (SAM) is expected to be neutral or weakly positive for the coming weeks. La Niña tends to favour positive SAM during spring and summer, which typically enhances the wet signal in the east.

The Madden–Julian Oscillation (MJO) is currently weak or indiscernible, but may increase in strength as it moves from the Maritime Continent 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.

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La Niña is a coupled ocean-atmosphere phenomenon that is the colder counterpart of El Niño, as part of the broader El Niño–Southern Oscillation (ENSO) climate pattern. – Wikipedia

via Tallbloke’s Talkshop

September 29, 2020 at 08:40AM