Tropical Climate Update

Climate conditions favour return of monsoon for northern Australia

Recent and developing conditions near Australian longitudes favour the formation of a monsoon trough over northern Australia in the coming fortnight. Tropical waves, other than the Madden–Julian Oscillation (MJO), have been a regular feature across the near-equatorial zone to Australia's north in the last fortnight, making environmental conditions favourable for enhanced cloudiness and rainfall. The resulting sustained humidity and build-up of deep cloud has led to a trough, running east-west, to the north of Australia. Favourable climate influences are likely to see it evolve into a monsoon trough in the next fortnight. If a monsoon trough develops and moves over the Australian mainland, significant rainfall could be expected over parts of northern Australia. An active monsoon trough also significantly increases the likelihood of tropical low and tropical cyclone formation.

Madden–Julian Oscillation approaches Australian region

The tropical waves discussed above were predominantly equatorial Rossby waves. They are related to MJOs, but are technically a separate type of wave or oscillation. Although the various tropical wave types have different features, they are alike in that they can significantly change the broadscale characteristics of a tropical environment. Depending on their location, these tropical waves can lead to either an increase or decrease in local cloudiness and rainfall.

In addition to the non-MJO waves, a moderate strength pulse of the MJO is currently tracking eastwards across the Indian Ocean, moving towards the Maritime Continent. At this time of the year, the influence of an MJO pulse can assist the formation or invigoration of a monsoon trough across northern Australia. Model outlooks suggest the MJO will move into a location that is favourable for enhanced cloudiness and rainfall over the Australian tropics in the next week or two.

Read more about the Bureau's current MJO monitoring.

Tropical cyclone focus shifts from Pacific to Indian Ocean

During the past week, there was tropical cyclone activity across the western Pacific Ocean in both the  northern and southern hemispheres. In the north, the very strong typhoon Wutip did not directly impact any populated land masses and dissipated over open waters to the east of the Philippines. In the southern hemisphere, tropical cyclone Pola peaked at category 4 strength on 28 February as it moved south of Tonga and Fiji, with sustained winds estimated at 165 km/h. Pola inundated parts of Samoa and American Samoa with heavy rainfall while it was a category 1 storm. Fiji and Tonga experienced strong to damaging winds and heavy rainfall as the severe tropical cyclone passed the island groups, but it did not directly cross over them. Pola rapidly weakened after attaining maximum intensity and dissipated by Saturday 2 March.

Aided by the presence of the MJO pulse, tropical cyclone Haleh developed well off the eastern coast of Madagascar in the southern Indian Ocean, on 2 March. Haleh is now moving to the southwest, well away from any land mass, and is expected to remain close to its current intensity, which is equivalent to an Australian category 4 tropical cyclone, before weakening in two or three days.

Further information on Haleh is available at the Meteo-France centre at La Réunion.