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Enso Outlook remains at La Niña Watch as Tropical Pacific cools, reports Bom

La Niña El Niño Enso

MELBOURNE, Australia – The El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are neutral, reports the Bureau of Meteorology of the Australian Government in its Climate Driver Update. The Bureau’s ENSO Outlook remains at La Niña WATCH, indicating the chance of La Niña forming in 2020 is around 50%— twice the average likelihood.

The surface and sub-surface of the tropical Pacific Ocean cooled significantly during autumn returning to near-average values. While the cooling trend eased during June, latest weekly values suggest a possible resumption of cooling has occurred in the tropical Pacific.

All surveyed international climate models anticipate further cooling is likely in the coming months with the majority of models exceeding the La Niña threshold during spring.

Other ENSO indicators, such as the Southern Oscillation Index (SOI), trade winds, and cloudiness near the Date Line, are also consistent with a neutral ENSO state, however the SOI has been steadily rising (consistent with a developing La Niña) since the beginning of July.

Much of the eastern Indian Ocean remains warmer than average although the possibility of a negative IOD developing by early spring has decreased with fewer models now suggesting its development.

Both La Niña and negative IOD typically increase the chance of above average rainfall across much of Australia during spring.

The Southern Annular Mode (SAM) is negative but is expected to increase to positive values by the end of July. In winter, a positive SAM typically reduces rainfall in far southern parts of the country, but can enhance rainfall in NSW and southern Queensland.

The Madden–Julian Oscillation (MJO) is weak and not having any significant influence on rainfall patterns across northern Australia.