Tropical Climate Update

Above-average tropical cyclone activity expected in 2022–23

The Bureau's Australian Tropical Cyclone Outlook was released on Monday 10 October. It forecasts a 73% chance of more than the average of 11 tropical cyclones (TC) in the coming season for Australia. The Eastern and Western sub-regions both have about 70% chance of above-average numbers while the Northern region is forecast to have a 61% chance—the Northern region is difficult to forecast, however, and the historical accuracy of the outlook in that region is relatively low.

While the long-term (since 1969–70) average number of TC in the Australian region is 11, there has been a notable decrease in seasonal TC numbers since about 2000; since the 2000–01 season, the average has reduced to 9 per season. Only once since 2000, in the 2005–06 season, have more than 11 TC been observed in the Australian region (there were 12 that season). Based on multiple current favourable climate drivers—La Niña, a negative Indian Ocean Dipole (IOD) event, and warmer-than-average sea surface temperatures around most of northern Australia—the 2022–23 season is likely to be the first season since 2005–06 when more than 11 TC are observed.

La Niña and negative IOD events have historically also been associated with early-season TC formation (i.e., during November compared to the usual early-December date), and an earlier date for the first landfalling TC (early-December compared to late-December).

The Bureau also issued a South Pacific Tropical Cyclone Outlook, which indicates an above-average number of TC in the western South Pacific region (65% likelihood), and a near-average number of TC in the eastern South Pacific region (43% likelihood) in 2022–23.

Read more about climate drivers in the Climate Driver Update

Madden–Julian Oscillation moves over the western Pacific Ocean

A pulse of the Madden-Julian Oscillation (MJO) strengthened as it moved through far eastern parts of the Maritime Continent, before progressing further east into the western Pacific region. While it strengthened rapidly last week, the pulse has already started to weaken. Most climate models predict the pulse will remain moderately strong as it tracks east towards the central Pacific region in the coming fortnight.

At this time of the year, although the influence of an MJO pulse located over the western Pacific region is mostly confined to northern parts of the Maritime Continent, north of Australia, it can increase the chance of above-average rainfall across parts of eastern Australia. An increase in westerly winds across the western Pacific is also associated with such a pulse, and this may have the effect of temporarily weakening equatorial trade winds in the region. The weakening of the trade winds is likely to be short-lived and not expected to adversely affect La Niña conditions in the Pacific Ocean (which can happen at certain times of the year with strong MJO activity).

Read more about the Madden–Julian Oscillation (MJO)