BAMOS May 2026
6 Article
“ Charts and Chocolate”: an overview of autumn weather events in Australia
Samuel Dahl, ARC Centre of Excellence for 21st Century Weather( s. dahl @ unsw. edu. au)
It’ s out with the tropical humid air from the north and in with the bursts of cold, polar air from the south. That’ s the topic of conversation in our weekly weather discussions at the UNSW Climate Change Research Centre this autumn. It’ s a recent endeavour to bring together our colleagues from diverse backgrounds of the climate-related sciences, including many AMOS members, to discuss the weekly weather in what we’ re calling“ Charts and Chocolate”.
As a recent arrival to Australia, I’ m still getting used to the diverse and exciting influences on our weather and climate here – from the cool-season mid-latitude weather characteristic of North America or Europe to the summer monsoon, which behaves like its counterpart in South Asia.
One of the regular activities from our weekly discussions is tracing the perceived boundary of polar and tropical air. As we moved from late summer to mid-autumn, this boundary gradually retreated northward, punctuated by sudden injections of cold, wintry air masses, and at times, still the tap of warm, moist air from the north. Fresh off a very wet summer for parts of central and northern Australia, along with these ups and downs have come several impressive weather systems.
In this article, we explore some of these recent events analysed during our discussions.
Tropical Cyclone Narelle
Despite reaching autumn, the tropical cyclone season extends until the end of April for northern Australia due to persistent high ocean heat content and remnant convection from the Australian monsoon. Cyclone Narelle was an extremely longlasting tropical cyclone in the second half of March, and you could say it made a grand tour, with four separate landfalls on the Australian coast over the course of its journey( Figure 1). These landfalls occurred in far-north Queensland, the Top End, the Kimberley, and eventually on the Northwest Cape of Western Australia.
After turning south around 26 March, Narelle weakened over land, and its remnants were swept up by the westerlies.
Many factors, including a lack of wind shear in the troposphere and large ocean heat content north of the continent, allowed Narelle to re-strengthen each time upon moving back over water. Narelle is only the second cyclone after Ingrid in 2005 to make severe landfalls( Category 3 or higher) in Queensland, the Northern Territory and Western Australia.
The impacts of Narelle included coastal erosion in all of the areas of landfall, flooding rains across the entire north of Australia and likely damage to coral reefs. One unique and eerie effect of Narelle was the appearance of red skies near Shark Bay, Western Australia, due to the lofting of red sediments into the atmosphere.
Early-season Tasman low
Also at the end of March, southeastern Australia experienced its first winter-like extratropical cyclone in the form of a rigorous Tasman low – a mid-latitude low-pressure system driven by baroclinic instability and strong temperature gradients. In this case, a low-pressure trough moved from Victoria and New South Wales over unusually warm waters off the coast, providing the right ingredients for the Tasman low to rapidly deepen( or“ bomb out”) through cyclogenesis. The tight pressure gradient off the coast of New South Wales resulted in very strong winds, with waves over 10 metres in the open ocean( Figure 2). For surfers along the coast, including in Sydney, this provided for once-in-a-lifetime surfing conditions. Following the passage of the Tasman low, a tongue of cold air extended poleward, and parts of Alpine Australia recorded their first snowfall of the season.
Figure 1: Depiction of Cyclone Narelle ' s track in the last two weeks of March. Credit: Bureau of Meteorology
Figure 2: Mean sea-level pressure analysis from midday local time on the 28th of March. The Tasman low is shown off the coast of New South Wales, while the remnants of Tropical Cyclone Narelle are located over Western Australia. Credit: Bureau of Meteorology