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BAMOS April 2025
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Other factors may also have been at play, including elevated sea surface temperatures over the northwest coast of Australia, which could have driven more evaporation. The moisture may have been transported towards North Queensland by strong westerly winds associated with an active Madden-Julian Oscillation.
The 2025 North Queensland floods serve as a reminder that weak low-pressure systems can still bring extensive amounts of rainfall, especially when they are slow-moving. While similar events occurred in recent years, including the 2019 floods in North Queensland and Tropical Cyclone Jasper in December 2023, it remains unclear whether these types of events will become more frequent with global warming. While the amount of moisture the atmosphere can hold increases with temperature, this does not necessarily translate into a comparable increase in rainfall. Some research also suggests that global tropical wind patterns may weaken as the Earth warms, slowing the movement of tropical cyclones and increasing rainfall. However, further research is required to determine whether this also applies to the weak tropical lowpressure systems over Australia.
Marine Heatwave off Western Australia
In addition to the North Queensland floods, this summer saw an intense marine heatwave, extending from Australia’ s northwest coast south along the Western Australian coast. The marine heatwave is likely linked to the deaths of 30,000 fish along the Pilbara coast and widespread coral bleaching across the Dampier Archipelago, Ningaloo Reef and Exmouth Gulf.
This marine heatwave began in September 2024, with sea surface temperatures up to 3 ° C above average, and dramatically intensified in late December before weakening in mid-February 2025( Figure 3).
Many areas along the Western Australian coast, particularly Shark Bay and waters off Port Hedland and Lombadina, recorded sea surface temperature anomalies at category 2( strong) and category 3( severe) marine heatwave intensity over these months( Figure 3). As of March, temperatures remain high along Australia’ s northwest coast and offshore waters, and the marine heatwave is ongoing.
This event is similar in scale to the 2010— 11 Western Australia( WA) marine heatwave, one of the most severe marine heatwaves recorded off Australia. If it persists or further intensifies, impacts such as those in 2011 may become evident, including seagrass loss, fisheries closures, and kelp forest dieback.
Unlike the 2010— 11 WA marine heatwave, which co-occurred with one of the strongest La Niñas on record, this summer’ s event developed under a“ weak” and seasonally late La Niña, suggesting additional factors may have contributed. Between December 2024 and January 2025, strong easterly wind anomalies over the equatorial western Pacific appear to have triggered downwelling westward-propagating Rossby waves. Upon reaching the western edge of the Pacific Ocean, these waves likely converted into downwelling coastal Kelvin waves and propagated through the Indonesian Archipelago and southward along the WA coast. As they propagate southward, these waves act to warm the waters of the WA coastal regions.
Additionally, local northerly wind anomalies off WA in December 2024 and January 2025 may have strengthened the Leeuwin Current— a strong ocean current that flows southward
Figure 3: Sea surface temperature anomalies( top) and marine heatwave extent and intensity category( bottom) from 1 January 2025 to 15 February 2025. Anomalies and marine heatwave detection are relative to the 1991 – 2020 baseline climatology. Credit: IMOS OceanCurrent SST product and the marine heatwave tracker.