Tropical Climate Update

Heavy rainfall over tropical Queensland eases

Coastal parts of tropical Queensland experienced very heavy rainfall during the past week. Widespread totals of more than 500 mm were recorded on the east coast between Mossman and Ingham. Some sites near Innisfail, the wettest region in Australia on average, had more than 900 mm during the week. The highest rainfall total of 926 mm was recorded at Topaz rainfall station. Significant flooding and infrastructure damage was widely reported across the region.

This section of the Queensland coast was the focus of the heavy rainfall due to its proximity to a developing monsoon trough, and a steady onshore flow of very humid air. In recent days, the monsoon trough was pushed north by a deep southeasterly wind-flow associated with a very strong high pressure system over southern Australia. This drier air has stemmed the heavy rainfall along the Queensland east coast.

The monsoon trough currently lies north of the Australian mainland, extending between a developing tropical low in the northern Coral Sea and the Arafura Sea, north of the Northern Territory (see latest chart here). This low has a moderate potential to develop into a tropical cyclone today (Tuesday), but the forecast track indicates it will rapidly move to the south where conditions will quickly become unfavourable for further strengthening. This low is unlikely to lead to a return of the heavy rain along Queensland's tropical north.

For up-to-date tropical cyclone information for the Australian region, please visit the Bureau's current tropical cyclones webpage.

Tropical wave activity strengthens monsoon trough

A pulse of the Madden–Julian Oscillation (MJO) over the Indian Ocean has become weak and is having little influence on northern Australian rainfall patterns. However, non-MJO tropical waves in the Australian region are having a discernible effect on northern Australia. International models agree the MJO will remain weak for at least the next seven days.

The atmospheric circulation associated with an equatorial Rossby wave in the western Pacific Ocean is invigorating the monsoon trough across Australia's north by increasing the cross-equatorial wind-flow in the region. This equatorial Rossby wave, which is a westward moving tropical pulse of low pressure, is forecast to aid the westward extension of the monsoon trough across the Timor Sea later in the week. Weather models suggest that other tropical lows may form along the monsoon trough, with the highest probability of formation being near the north coast of the Northern Territory. However, model uncertainty suggests tropical lows could form in any region between the northern Kimberley of Western Australia to Cape York Peninsula in Queensland in the coming week.

Equatorial Rossby wave activity is also evident across the Indian Ocean where an out-of-season tropical low has recently developed in the northern hemisphere, south of India. This low is the northern hemisphere pair of a second Indian Ocean low in the southern hemisphere. These lows straddling the equator are typical of the mirroring low-pressure pairs that are a defining feature of equatorial Rossby waves.

See the Bureau's current MJO monitoring for more information.

Pacific Ocean returns to neutral; La Niña ends

La Niña has ended, as the El Niño-Southern Oscillation returned to a neutral state, with the tropical Pacific Ocean warming since late December. Waters beneath the surface have also warmed, and atmospheric indicators such as the Southern Oscillation Index (SOI) are firmly in the neutral range.

See the Bureau's current ENSO Wrap-Up for more information.