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ENSO Outlook raised from ‘La Niña WATCH’ to ‘La Niña ALERT’

chance of above median rainfall september to november 2022 f

The Australian Bureau of Meteorology (BOM) has raised the ENSO Outlook status from ‘La Niña WATCH’ to ‘La Niña ALERT’ with the likelihood of La Niña returning this spring increasing to around 3 times the normal risk.

  • This status change follows a renewal of cooling in the tropical Pacific Ocean towards La Niña thresholds over recent weeks, as well as the persistence of the Southern Oscillation Index (SOI) at La Niña levels and strengthened trade winds at La Niña levels.
  • Climate models indicate further cooling is likely, with four of seven models suggesting La Niña could return by early-to-mid southern hemisphere spring.

Climate models and indicators have shifted towards meeting La Niña ALERT criteria which means the chance of a La Niña developing in the coming season has increased, BOM said in a report issued on August 16, 2022.1

When La Niña criteria have been met in the past, a La Niña event has developed around 70% of the time.

La Niña refers to changes in sea surface temperatures in the tropical Pacific Ocean, with waters in the eastern Pacific being cooler than normal, and waters in the western tropical Pacific being warmer than normal.

During this period, trade winds strengthen, increasing the water moisture in the air, which usually brings rainfall to eastern and central Australia and a wetter start to the northern wet season.

The Bureau’s 3-month climate outlook shows a high chance of above-average rainfall for most of the eastern two-thirds of the Australian mainland between September and November 2022. The outlook reflects a range of climate drivers, including a negative Indian Ocean Dipole (IOD) event and warmer than average waters around Australia.

With wet soils, high rivers and full dams, and the outlook for above-average rainfall, elevated flood risk remains for eastern Australia.

Some third-party sources and media outlets have suggested that the east coast of Australia is experiencing a third La Niña. This reporting does not reflect the complexity of Australia’s climate and is not entirely accurate.

The Bureau of Meteorology’s El Niño–Southern Oscillation Outlook, which is monitored by the Bureau’s specialist climatologists and is underpinned by an analysis of seven climate models, is at La Niña ALERT status. This means there is a 70% chance of La Niña returning this spring.

The Bureau is advising of very high chances of wet conditions over eastern Australia for the next three months. Should a La Niña event be established in the Pacific Ocean, the wet conditions will persist into summer.

This rainfall outlook is of great importance to communities in eastern Australia given the increased risk of flood following above-average rainfall for the past few months and above-average soil moisture levels.

BOM is urging communities living in the affected regions to keep up to date with official forecasts and warnings on the Bureau’s website and BOM Weather app and follow the advice of emergency services.

References:

1 Climate Driver Update – Wet outlook continues with an increased chance of La Nina developing this spring – BOM – August 16, 2022

Featured image credit: BOM (chance of above median rainfall for September and October 2022).

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