Tropical Climate Update

Climate driver influence on northern Australia

The 2021–22 La Niña has dissipated, with most indicators now depicting a neutral ENSO state (neither La Niña nor El Niño). However, some model outlooks suggest La Niña may re-form from spring 2022. As a result, the Bureau's ENSO Outlook status has moved to La Niña WATCH. La Niña WATCH means there is around a 50% chance of La Niña re-forming in 2022. This is approximately double the normal likelihood.

If La Niña redevelops in 2022, many parts of northern Australia would most likely see above-average rainfall in the early wet season period, potentially as early as September (the official northern wet season is October to April). La Niña typically also leads to above-average temperatures, particularly night-time temperatures, during the winter-spring period. Tropical cyclone (TC) activity across northern Australia is also influenced by La Niña, with the first TC of the TC season (November to April) often developing earlier than average. A La Niña wet-season period (October to April) typically sees average to above-average numbers of TCs. However, in recent years this has been moderated by the downwards trend in TC activity in the Australian region since 2000.

The Indian Ocean Dipole (IOD) index has been near or below the negative IOD threshold in the last 3 weeks. A negative IOD event is generally considered to have developed when the index has been close to or below the IOD threshold for around 8 weeks. Climate models indicate a negative IOD is likely to develop over winter.

Similar to the influence of La Niña, a negative IOD normally leads to above-average rainfall in the early wet-season period across much of northern Australia, although to a lesser extent than La Niña. When it comes to temperature, however, a negative IOD typically has a stronger influence than La Niña in producing warmer days and nights in the winter-spring period. The influence exerted by the negative IOD usually diminishes significantly by the end of spring or start of summer, and so while it has an influence on tropical cyclone activity around northern Australia, it is usually confined to increasing the likelihood of a first TC developing earlier than average.

Read more about climate drivers

Madden–Julian Oscillation in Indian Ocean

After stalling in the Africa region last week, a moderately strong pulse of the Madden-Julian Oscillation (MJO) tracked eastwards, into the tropical western Indian Ocean in recent days. While this pulse of the MJO is forecast to weaken slightly in the coming days, most climate models indicate it will remain as a coherent and discernible pulse of the MJO and track further east into the eastern Indian Ocean in the coming week.

At this time of the year, the influence on tropical rainfall patterns of an MJO pulse over the Indian Ocean is generally confined to north of the equator, although some parts of north-eastern Australia and the northern Maritime Continent are favoured to have above-average rainfall in this scenario.

Looking at the broadscale influence of the MJO in the coming fortnight, there is an increased likelihood that stronger-than-average trade winds (easterly winds) will prevail cross the tropical central and western Pacific Ocean. As a result, some La Niña indicators may briefly move closer to La Niña thresholds.

Read more about the Madden–Julian Oscillation (MJO)