Tropical Climate Update

Tropical weather focus shifting to southern hemisphere

The tropical transition period, when the focus of tropical weather moves from the northern to southern hemisphere, is well underway. As solar heating lessens in the north and increases south of the equator, energy to fuel the heating of oceans and broadscale weather systems increasingly affects the southern hemisphere. In recent weeks, near-equatorial troughs have become apparent in both hemispheres over the Indian Ocean and the Maritime Continent, shown in this gradient wind analysis chart. This is a typical feature of the transition period, and while significant tropical weather is apparent over parts of India and South-East Asia, this will become increasingly uncommon in the coming weeks. The Southwest Indian Monsoon withdrew from India at the end of October and weaker tropical troughs, like that currently affecting southern India, will become less frequent in the lead-up to India's dry season (December-March).

Weak Madden–Julian Oscillation in Australian region

A relatively weak pulse of the Madden–Julian Oscillation (MJO) has tracked eastwards across the Maritime Continent, to Australia's north, in recent days. It is likely that the MJO aided the development of the near-equatorial troughs, and the general increase in cloudiness and rainfall across the tropical eastern Indian Ocean. Satellite imagery displays significant cloud associated with the near-equatorial troughs in both hemispheres. In the southern Indian Ocean, tropical low activity has developed in the trough to the southwest of Sumatra. A weak tropical low may form near Christmas Island in the next few days, and while it is unlikely to develop significantly, it may generate significant rainfall over the Island.

Climate models predict the MJO pulse will become indiscernible in the coming days. As a result, the MJO is unlikely to have a significant influence on rainfall patterns across the region apart from the current surge in weather across the tropical Indian Ocean.

Read more about the Madden–Julian Oscillation (MJO)

La Niña-like rainfall pattern in climate models

The latest rainfall outlooks from the Bureau depict 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. 

Indicators of the El Niño–Southern Oscillation (ENSO) show some shifts towards a La Niña-like state, with cooler than average ocean temperatures across the tropical Pacific Ocean and warm waters around northern Australia. All climate models surveyed by the Bureau indicate La Niña is likely to develop in the coming weeks. The rainfall outlook is also consistent with the decreased influence from the negative Indian Ocean Dipole (IOD) which has been relatively weak for the last 2 months. The IOD is forecast to return to neutral levels in the coming weeks.

Consistent with the climate outlooks, La Niña increases the likelihood of above-average rainfall for northern Australia during the wet season (October–April). La Niña is also typically associated with an earlier-than-normal monsoon onset at Darwin and increased tropical cyclone activity across the Australian region.

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