Weekly Tropical Climate Note

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Monsoonal conditions redevelop over northern Australia

Most international models monitored by the Bureau predict the current burst of monsoonal activity over northern Australia will persist for the coming week. In the short term, the focus of the monsoonal activity will be northern Western Australia, associated the slowly intensifying monsoon low, but there is uncertainty in the longer term as to where the main focus will be.

In recent weeks, a relatively brief monsoonal burst impacted parts of northern Australia between 21 and 24 December. Moderate rainfall totals were recorded in the Northern Territory’s Top End and the northern Kimberley of Western Australia. Two significant tropical lows developed within the monsoon trough over northwestern Australia. One of the lows, off the Western Australia coast, briefly developed into tropical cyclone Yvette, the first tropical cyclone of the 2016–17 Australian tropical cyclone season. The second low remained over land after initially developing over the western Top End.

On 25 December these two lows combined into one tropical depression, inland of the Pilbara coast in Western Australia. At the same time, the monsoon trough temporarily withdrew from the Australian continent. However, high levels of deep-layer moisture associated with the northwesterly monsoonal flow followed the tropical depression as it tracked to the southeast, delivering heavy rainfall and widespread flooding over parts of central Australia.

Another monsoon trough developed over northeastern Australia on 28 December, and gradually extended west to a low pressure system currently lying over the western Top End. There remains a heightened risk of cyclone development in the Australian region with an active monsoon trough over northern Australia. However, most models do not predict any cyclone development in the coming days. For more information on all tropical systems affecting the Australian region, please check the Bureau’s tropical cyclones webpage.

Madden–Julian Oscillation not the primary driver of monsoonal activity

The recent monsoonal activity in the Australian region developed while the Madden–Julian Oscillation (MJO) was weak or indiscernible. An extended period of stronger than average northeast tradewind flow has been evident in the North Pacific Ocean and, combined with enhanced westerly winds across the eastern tropical Indian Ocean, provided much of the energy which initiated and continues to maintain the monsoon trough in the southern hemisphere.

In the northern hemisphere typhoon Nina (Nock-Ten) impacted the northern Philippines on Christmas Day, causing multiple fatalities and widespread disruption.

Most models agree that the MJO signal is likely to remain relatively weak in the coming week with its exact evolution and location still to be determined.

See the Bureau's current MJO Monitoring information.

ENSO-neutral conditions to continue

The El Niño–Southern Oscillation (ENSO) in the tropical Pacific Ocean remains neutral, and most climate models suggest this will remain the case throughout the Austral summer. Ocean temperatures and atmospheric indicators remain well within the neutral range.

See the Bureau’s ENSO Wrap-Up for official El Niño, La Niña and IOD information.

Product code: IDCKGEW000