Tropical Climate Update

Imogen gives way to monsoon break across northern Australia

Ex-tropical cyclone (TC) Imogen and associated low-pressure troughs generated heavy rain across the tropical coast of eastern Queensland during the past week. The coastal strip between Cooktown and Mackay, along with the region near the base of Cape York Peninsula where Imogen traversed, saw widespread 7-day (to 11 January) rainfall totals in excess of 200 mm. The highest weekly total to 11 January was at Gairloch, near Ingham, with 550.2 mm. Significant disruption due to riverine flooding was also experienced across parts of northern Queensland.

Ex TC- Imogen has moved off the Queensland coast and weakened, and is not expected to significantly affect the tropical coast of Queensland in the coming days. Along with the rest of northern Australia, tropical Queensland is likely to be dominated by easterly trade winds in the coming week. These will contribute to further shower activity for eastern Queensland, but maintain relatively settled conditions across other parts of the Australian tropics. When trade winds dominate northern Australia at this time of the year, the monsoon is classified as inactive—this phase of the Australian monsoon is also known as a monsoon break.

While Australia is experiencing monsoon break conditions, a monsoon trough lies over the Indian Ocean, extending from south of Java, Indonesia, towards the central Indian Ocean. A tropical low within the monsoon trough, well west of Australia, has the potential to intensify, but is forecast to move further away from the Australian coast in the coming days.

Monsoon conditions may redevelop across Australia in the next fortnight

Climate and weather models indicate that a monsoon trough may develop across Australian longitudes in about a week, as broadscale atmospheric conditions become favourable for increased tropical weather. If a monsoon trough moves over northern Australia, the monsoon phase would change from break to active, and widepsread rainfall and tropical cyclone development would become more likely.

The change from a break to an active monsoon is typically induced by changes in the tropical wind patterns around Australia's longitudes or the influence of an approaching tropical atmospheric wave, such as the Madden–Julian Oscillation (MJO).

Madden–Julian Oscillation strengthens over the Indian Ocean

A pulse of the Madden–Julian Oscillation (MJO) has strengthened over the Indian Ocean in the past week. While the climate models surveyed by the Bureau indicate eastwards movement, there is disagreement amongst models as to the forecast strength of the MJO pulse in the coming fortnight.

Combined with another type of tropical atmospheric wave, an equatorial Rossby wave, the MJO is likely to contribute to an increase in tropical convection and rainfall and an above-average tropical cyclone risk around northern Australia in about a week. This is reflected in the latest climate outlook released by the Bureau, which shows a strong signal for above-median rainfall in the period 16–29 January.

Read more about the Madden–Julian Oscillation

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