But the patterns involve a lack of wind rather than extreme heat alone, and scientists say studying atmospheric conditions could help them predict future mass bleaching events.
Researchers from Monash University and the University of Melbourne revealed the findings on Monday in a scientific paper that examined almost three decades of weather data.
It comes after the Bureau of Meteorology confirmed El Nino conditions were nearing record levels, and surface temperatures in the Coral Sea were expected to warm over the coming months.
The research, published in Weather and Climate Dynamics, analysed atmospheric data collected from the Great Barrier Reef between 1996 and 2024.
It examined periods of weak winds, reduced cloud cover and dry air known as the doldrums, which can cause ocean temperatures to rise off north Queensland.
These conditions reduce the cooling effect of easterly trade winds, allowing heat to build up and raising the risk of marine heatwaves during El Nino conditions.
Risks to the Great Barrier Reef increased when the doldrums persisted, Monash University researcher Dr Lara Richards said, and the study sought to identify why some periods lasted longer than others.
"When doldrums hang around, the ocean remains in a heating phase for longer, which can produce rapid increases in temperature and contribute to bleaching," she said.
Researchers found that low-pressure systems that stall over eastern Australia, combined with high-pressure systems near New Zealand, could prolong the dangerous conditions.
The phenomenon occurred in early 2022, Dr Richards said, when low-pressure systems delivered persistent heavy rain over NSW and southern Queensland and contributed to dry conditions over the reef.
"The Lismore floods are a striking example of how the same weather system can produce very different conditions across Australia," she said.
"While the low-pressure system draws moist air south towards the east coast, its circulation can also steer dry air north across the continent and towards the Great Barrier Reef."
The event occurred during a La Nina phase, the study said, showing the phenomenon could develop outside El Nino conditions.
The study's findings could help researchers identify future coral bleaching risks, University of Melbourne climate science senior lecturer Dr Yi Huang said.
"The next question is whether we can predict these events using the computer models and tools we already have," she said.
"Ultimately, understanding coral bleaching events will require high-resolution coupled climate models that allow the atmosphere and ocean to interact directly."
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