Tropical Climate Update

First tropical cyclone for Australia in 2021–22

Tropical cyclone Paddy was named on the morning of 22 November 2021. Paddy formed along a low-pressure trough which extended from the south-eastern Indian Ocean to north of Australia. Paddy did not strengthen beyond category 1 intensity, and remained at tropical cyclone strength for less than 2 days before it dissipated. Paddy did not directly impact either the Australian mainland or its territories. However, Christmas Island did observe significant rainfall generated in the vicinity of the trough which spawned Paddy. Perhaps Paddy's most significant feature was its date of formation—November tropical cyclones are relatively infrequent in the Australian region.

The likelihood of a November tropical cyclone in the Australian region increases when La Niña is active. Similarly, the onset of the Australian monsoon at Darwin is typically earlier than the average date during La Niña, occurring closer to mid-December than the usual late December date.

A low-pressure trough remains just south of the equator over the south-eastern Indian Ocean and has recently extended further east into the region north of Australia. This trough, along with low pressure over northern Australia, and the location of the Madden–Julian Oscillation, means conditions are broadly favourable for the formation of a monsoon trough in the southern hemisphere.

Madden–Julian Oscillation strengthened over Australian region

In the past fortnight, a moderately strong pulse of the Madden–Julian Oscillation (MJO) was located over the Maritime Continent, to Australia's north. This pulse was likely a significant contributing factor in the formation of tropical cyclone Paddy, by providing conditions favourable for the development of the near-equatorial trough in the south-eastern Indian Ocean.

The current MJO pulse has weakened in recent days but is expected to track eastwards across the Maritime Continent and restrengthen in the coming week while in the Western Pacific region. In this scenario, the MJO is likely to increase the chance of above-average cloudiness and rainfall over far northern Australia and the Maritime Continent. At this time of year, an MJO in these regions also increases the chance of broadscale westerly wind-flow developing over the region, including around northern Australia. As such, the MJO may assist the development of monsoonal flow in the southern hemisphere across Maritime Continent longitudes.

Read more about the Madden–Julian Oscillation (MJO)

La Niña established in the tropical Pacific

La Niña has become established in the tropical Pacific. Climate models suggest this La Niña will persist until at least the end of January 2022. La Niña events increase the chance of above-average rainfall across much of northern and eastern Australia during the summer months.

The latest rainfall outlooks from the Bureau reflect a seasonal signal that broadly resembles a typical La Niña rainfall pattern, with a high chance of above-median rainfall across much of eastern Australia, including Queensland, and roughly equal chances of above- or below-median rainfall across the Northern Territory and northern Western Australia. 

Typically, rainfall across northern Australia is above average during the northern wet season (October–April) in La Niña years, as is the likelihood of increased tropical cyclone numbers, compared to all years. Along with an early first tropical cyclone, the first tropical cyclone to make landfall on the Australian coast usually occurs earlier than average. The only time (since around 1970 when reliable records became available) multiple severe tropical cyclones have impacted the Queensland coast was during La Niña years.

Read more about the current climate drivers in the Climate Driver Update