Tropical Climate Update

Monsoon trough develops off northwest Australia

In recent days a monsoon trough formed over waters between Indonesia and the coast of north-western Australia. The north-westerly monsoonal winds associated with the trough are currently relatively weak and are confined to a small region over water, to Australia's northwest.

A monsoon trough is typically a favourable region for the development of tropical lows and tropical cyclones, and the latest weather chart indicates 2 weak tropical lows have recently formed to Australia's northwest. Current weather model guidance and forecaster assessment indicates there remains a low risk that either of these lows will intensify to tropical cyclone strength in the coming week.

Depending on where the tropical lows move, they may drag the monsoon trough onto the Western Australia (WA) coast, and lessen the likelihood of monsoonal conditions extending further east into the Northern Territory or Queensland, in the coming week. As a result, official monsoon onset for Australia, which is measured at Darwin Airport, may not occur in the next week. This scenario would likely mean parts of northern WA observing large rainfall totals in the coming week; a Severe Weather Warning has been issued for heavy rainfall.

Read more about Australian tropical cyclone outlooks

Madden–Julian Oscillation in Australian region

The formation of the monsoon trough off north-western Australia is associated with a pulse of the Madden–Julian Oscillation (MJO), in combination with other tropical atmospheric waves in the region. These short-term climate influences have made conditions around northern Australia and parts of the Maritime Continent conducive to widespread rainfall and the development of monsoonal conditions over northern Australia.

The relatively weak Madden–Julian Oscillation (MJO) pulse, which currently lies over the Maritime Continent, to the north of Australia, is expected to slowly track further east during the coming fortnight, at a similar strength. Along with an equatorial Rossby wave, this MJO pulse is expected to help maintain environmental conditions favourable to above-average rainfall around north-western Australia in the coming week. There is also the potential for significant rainfall to affect parts of the Northern Territory and possibly some parts of Queensland, the following week.

Apart from the impact monsoonal conditions would have on northern Australia, the moisture drawn from the tropical oceans to Australia's north could potentially be a source for rainfall over more southern parts of Australia. With favourable weather systems across southern Australia during the next fortnight, this may contribute to the forecast wetter conditions expected across much of the continent during December.

Read more about the Madden–Julian Oscillation