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Positive IOD likely for winter, El Niño Watch remains, reports Bom

Indian Ocean Dipole

MELBOURNE, Australia – The tropical Pacific Ocean and atmosphere remain near El Niño thresholds, meaning the ENSO Outlook remains at El Niño Watch, reports the Australian Government Bureau of Meteorology (BOM) in its latest report. Climate models suggest a gradual shift away from El Niño levels over the coming months.

Indian Ocean temperature forecasts, on the other hand, show a positive Indian Ocean Dipole (IOD) through the southern winter, which is likely to be the dominant climate driver for Australia.

A fortnight ago, a pulse of the Madden–Julian Oscillation (MJO) weakened trade winds, which led to some renewed warming at the surface of the tropical Pacific Ocean. However, this MJO pulse has passed, returning trade winds to normal levels. With little warmth in the ocean sub-surface, most climate models suggest the tropical Pacific will cool, shifting away from El Niño thresholds, during winter.

In the Indian Ocean, waters off Sumatra have cooled over the past fortnight, with the IOD index now exceeding positive thresholds for three weeks. All but one of the climate models suggest positive IOD values will persist through winter and into spring.

To be considered a positive IOD event, positive thresholds need to be maintained for at least two months. Typically, a positive IOD brings below average winter-spring rainfall for southern and central Australia. This is currently being reflected in the rainfall outlook for the coming months.