Tropical Climate Update

Madden–Julian Oscillation moves into Australian region

A weak pulse of the Madden–Julian Oscillation (MJO) moved into Maritime Continent, north of Australia, during the past week. This pulse is expected to remain relatively weak, although climate models indicate different possible movement scenarios for the pulse in the coming fortnight. Some indicate the MJO will stall, while others suggest further eastwards movement. Most of the predictions, however, maintain the MJO pulse in a region that favours above-average cloudiness and rainfall across parts of northern Australia and the Maritime Continent.

The location of the MJO, and the time of the year, also points to favourable circumstances with respect to the development of monsoon conditions across the northern Australia region. Historically, even weak pulses of the MJO, in a favourable location, are associated with monsoon onset at Darwin. The average date of monsoon onset during La Niña years is mid-December. Recent tropical pressure and wind patterns are also indicative of broadscale changes conducive to the development of monsoonal conditions across the Australian region in the coming weeks.

Apart from the impact a monsoon would have on northern Australia, it could potentially transport significant amount of moisture to parts of Australia further south, and contribute to the forecast wetter conditions expected across much of the continent during December.

Read more about the Madden–Julian Oscillation

Increased tropical cyclone risk for northern Australia

As the prospect of monsoonal conditions in the Australian region increases, so does the risk of tropical cyclone (TC) development. A monsoon trough near northern Australia is often a focus region for tropical low or TC formation at this time of the year.

Tropical cyclone computer model guidance suggests an increased, but relatively low, risk of a TC forming over waters to the northwest of Australia in the coming week, becoming more likely in the following week.

TC and tropical low numbers across the Australian region are typically higher when La Niña is active, compared to non-La Niña years. The most recent national TC Outlook released by the Bureau indicates a 66% chance of above-average TC numbers during the 2020–21 season. In La Niña years, the first TC usually forms earlier than normal, on average around mid-December, while the date of the first landfalling TC to impact Australia is also earlier than usual, occurring around early January. The only recorded instances of more than one severe (category 3 or greater) TC making landfall on Queensland have been when La Niña was active.

Read more about Australian tropical cyclone outlooks