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North Queensland Heavy Rain Set to Stay - The Tale of a Fractured MJO

Weatherwatch

February 5, 2025


The monsoon was late this year, but now that it's arrived, it's unlikely to shift anytime soon, raising concerns for flooding and prolonged heavy rainfall across northern Australia. The monsoon is not unusual, but the persistence of a convergence line is unusual and is causing particular concerns for areas of northern Queensland.


Next 7 day rainfall from EC - rainfall heavily favouring northern Australia though indirectly, some showers and storms will occur across parts of southeastern to eastern Australia. Source: Weatherwatch MetCentre.


A Late but Intense Monsoon


The Australian monsoon typically arrives in late December or early January, but this summer, it was delayed until late January—far later than usual. The monsoon develops when heat builds over the continent, creating low pressure that draws in moist ocean air, fueling showers and storms. This process often needs a trigger, such as a pulse of the Madden-Julian Oscillation (MJO) - which is a burst of westerly winds that sweeps across tropical northern Australia every 30-60 days during the Southern Hemisphere summer.


However, this time there's some additional factors at play.


A Fractured MJO is Causing Havoc in Northern Queensland


Firstly - let's understand how the MJO works to increase rainfall. The westerly winds push against the trade southeasterlies and this convergence generates rainfall. Further, the general westerly flow is often humid and unstable and this can generate rainfall also. Normally, the westerly winds from the MJO are stronger than the trade winds - this allows the MJO to continue to track eastwards until it finally weakens out over the Pacific Ocean.


The MJO produces elevated rainfall due to a clash of westerly winds colliding with the trade winds. Source: BoM
The MJO produces elevated rainfall due to a clash of westerly winds colliding with the trade winds. Source: BoM


However, this MJO has been a bit different - and one of the key differences lies with the development of Tropical Cyclone Taliah and Tropical Cyclone Vince in the Indian Ocean. These two tropical cyclones have been moving westwards meaning that the MJO has become fractured. There's the initial burst of westerly winds across northern Queensland, and then the stronger burst of westerly winds are entangled with the tropical cyclones in the Indian Ocean.


Tropical Cyclone Taliah and Vince have helped fracture the MJO pulse, meaning that a weaker westerly burst is currently located over northern Australia which is approximately the same strength as the trade winds from the southeast causing heavy rain across northern Queensland. Source: Weatherwatch MetCentre.


The result is that the westerly winds across northern Queensland are approximately the same strength as the trade winds coming in from the southeast. So instead of the convergence between the MJO and the southeasterly trade winds tracking eastwards like it should, it's stalled across northern Queensland and the boundary between these two airmasses doesn't look like shifting anytime soon.


EC winds from today vs Saturday showing the convergence boundary between the monsoonal northwest winds and the southeasterly trade winds does not shift. Source: Weatherwatch MetCentre.


High Temperatures Providing Additional Fuel for the Monsoon Trough


The monsoon trough is a frequent visitor to northern Australia during the second half of summer and doesn't normally clear until late March. The monsoon is driven by the temperature difference between the oceans and land. As the monsoon was late this year, there's been additional heat buildup - and now all that heat is helping to fuel a stronger monsoon trough.


January was hot across much of Australia. This heat is helping to fuel the monsoon trough. Source: BoM
January was hot across much of Australia. This heat is helping to fuel the monsoon trough. Source: BoM


No End in Sight to North Queensland Rainfall - Further Rain for Northern Australia


For parts of northern Australia, this will be a classic wet season—flooded roads, restricted access, and travel disruptions - nothing too unusual. However, in areas that already received significant rainfall, such as flood-affected regions of northeastern Queensland, there is serious concern for renewed flooding as the boundary between the onset of the monsoon and MJO, continues to collide with the trade winds coming in from the southeast.


EC rainfall continues to favour northern Queensland for further heavy falls during the next 7 days. Source: Weatherwatch MetCentre.


At this stage, there is no current indication that the monsoon will push further south, but history suggests that active monsoonal periods often increase rainfall across southern Australia as well. The longer the monsoon trough remains active across northern Australia, then the higher the chance of moisture and rainfall tracking southwards will be.


Uncharted Territory? The Role of Warmer Oceans


The past few years have seen exceptionally warm ocean temperatures around Australia. Since the monsoon is largely driven by the temperature contrast between land and ocean, it remains uncertain how these warmer waters might impact future monsoonal patterns. What we do know is that warmer oceans can fuel more intense rainfall due to higher precipitable water values. We certainly saw this occur across northeastern Queensland with locations near Rollingstone recording 1700mm in just 72 hours - the equivalent of a "1 in 2000 year" rainfall event!


Even by north Queensland standards, the rainfall has been exceptional with falls of more than 1700mm occurring in just 72 hours. The equivalent of a 1 in 2000 year rainfall event. Source: BoM
Even by north Queensland standards, the rainfall has been exceptional with falls of more than 1700mm occurring in just 72 hours. The equivalent of a 1 in 2000 year rainfall event. Source: BoM

For now, the monsoon is expected to remain active through February, with an elevated risk of tropical low or cyclone development. Once the MJO shifts out of phase later next month, the potential for high levels of rainfall across northern Australia rainfall should gradually decrease—but until then, northern Australia should remain on high alert for heavy rain and flooding.


The current MJO period should shift out of phase towards the latter part of February, resulting in tropical activity gradually easing across northern Australia. Source: BoM
The current MJO period should shift out of phase towards the latter part of February, resulting in tropical activity gradually easing across northern Australia. Source: BoM

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