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Negative Indian Ocean Dipole possible in 2020, says Bom in its new report

La Niña

MELBOURNE, Australia – The El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) remain neutral, reports the Australian Government Bureau of Meteorology in its Enso Wrap-Up. While neutral ENSO is likely for the southern hemisphere winter, some model outlooks suggest a La Niña-like state will develop in the tropical Pacific Ocean during spring. Most models suggest a negative IOD will develop in the Indian Ocean from mid-winter, but model skill is low at this time of year.

The IOD is currently neutral. Most international climate models surveyed by the Bureau suggest the development of a negative IOD from the middle of the southern hemisphere winter. However, each of the models show a broad spread of likely scenarios between the neutral IOD and negative IOD range, and more recent model outlooks having slightly lower likelihoods of negative IOD. Accuracy of IOD forecasts is low for forecasts made during autumn, with accuracy improving in winter. A negative IOD typically brings above average winter–spring rainfall to southern Australia.

Key indicators of ENSO, such as the Southern Oscillation Index (SOI), trade winds, cloudiness near the Date Line and sea surface temperatures in the tropical Pacific Ocean, generally persist at neutral ENSO levels. However, sea surface temperatures across the tropical Pacific Ocean have cooled over the past several weeks. This has been supported by recent cooling of tropical Pacific sub-surface temperatures.

International climate models surveyed by the Bureau indicate that ENSO is likely to stay neutral through the southern hemisphere winter. However, by early-to-mid spring, three models of the eight models currently reach or exceed La Niña levels. Like model outlooks for the IOD, ENSO predictions made during autumn tend to have lower accuracy than predictions made at other times of the year. This is because development of both ENSO and the IOD have greater sensitivity to random weather factors at this time.

The Bureau’s ENSO Outlook is currently at INACTIVE. However, if recent cooling at both the surface and beneath the surface of the tropical Pacific Ocean persists, and any more models suggest La Niña-like conditions in spring, the ENSO Outlook will shift to La Niña WATCH.

The Southern Annular Mode (SAM) is currently positive and forecast to remain positive for the coming two weeks. However, it isn’t expected to have a significant effect on rainfall during this time due to interactions with other climate drivers and local weather conditions.