Every year, Northern Australia eagerly anticipates the arrival of the summer monsoon, a critical weather event characterized by a reversal of winds, heavy rainfall, and occasional flooding. However, the 2024-2025 Australian summer monsoon (ASM) was the latest on record since measurements began in 1957. This unprecedented delay has significant implications for the region’s water security, agriculture, and fire risk management.
The monsoon’s timely arrival is essential for Northern Australia. It dictates water availability for communities, supports pasture growth crucial for the cattle industry, and marks the end of the high bushfire risk period. Typically, the ASM begins with a shift from the prevailing dry southeasterly trade winds to moist northwesterly winds, first observed over Darwin, the northernmost city in Australia, around Christmas and the New Year.
Record Delay Despite Favorable Conditions
In a surprising turn of events, the ASM onset occurred on February 7, 2025, more than five weeks later than usual and over two weeks later than the previous record set in the 1972-1973 season. This delay occurred despite favorable large-scale climate conditions, such as a La Niña-like state in the Pacific Ocean, record ocean warmth, and strong ocean convection in December.
To uncover the reasons behind this delay, an international research team led by the University of Southern Queensland investigated the monsoon criteria and local weather conditions affecting the ASM onset. Their findings were published on January 29 in Advances in Atmospheric Sciences as part of a special issue by the World Climate Research Programme’s monsoon panel.
Investigating Local vs. Regional Conditions
The research team, led by Associate Professor Tim Cowan, sought to determine whether the record-late onset was a genuine feature of the broader monsoon system or a result of local wind conditions in Darwin. “We wanted to understand if this was a broader monsoon feature or isolated to Darwin,” Cowan explained. The team compared various monsoon onset definitions across Northern Australia and analyzed atmospheric processes before and during the onset period.
Importantly, the study revealed that the conditions in Darwin during the summer of 2024-2025 did not necessarily reflect other parts of Australia.
“The record-late ASM onset in 2024/25 was not entirely representative of the broader monsoon conditions across all of northern Australia but only specific to local wind conditions over Darwin,” said Rajashree Naha, a research fellow and co-author of the study.
This suggests that local weather variability over Darwin prevented the upper-level winds from switching to easterlies, despite strong westerlies in December.
Implications for Weather Communication
The research team hopes their findings will enhance weather communication with the public. “Often people (and the media) confuse the official monsoon onset, based on local winds, with the onset of the first monsoonal rains,” Cowan noted. The study provides an opportunity to improve messaging about monsoon arrival and its impacts on local communities.
Ultimately, the research emphasizes the importance of clear, actionable information for communities dependent on the monsoon. The team believes their work could improve preparedness across Northern Australia, ensuring residents and industries receive timely and accurate forecasts.
Looking Forward: Monitoring the 2025-2026 Season
As the 2025-2026 wet season unfolds, communities and forecasters are once again closely monitoring Darwin’s winds. This serves as a reminder of how critical clear and accurate monsoon onset information is for Northern Australia each year. The ongoing research and improved understanding of monsoon dynamics are vital for the region’s resilience and adaptation to climate variability.
The study was a collaborative effort involving researchers from the Bureau of Meteorology, the University of Melbourne, Monash University, and the Institute of Atmospheric Physics in Beijing, among others. It was supported by Meat & Livestock Australia, the Queensland Government, and the University of Southern Queensland through various climate programs.
