Australia's East Coast is bracing for a powerful display of nature's might, with strong waves set to crash upon its shores over the coming fortnight. This phenomenon is not merely a coastal curiosity; it's a potential threat with intriguing meteorological origins.
The catalyst: Tropical cyclone activity is on the rise in the Coral Sea and the southwest Pacific Ocean, and computer models predict the formation of tropical lows or cyclones in the region over the next two weeks. This forecast is supported by the presence of an active Madden-Julian Oscillation (MJO) phase, which is known to boost cloud and thunderstorm activity, potentially leading to the development of tropical cyclones.
A warm ocean's role: The ocean's surface temperatures play a crucial part in this story. Currently, the waters across the Coral Sea and southwest Pacific are unusually warm, influenced by weak La Niña conditions. These warm seas, exceeding 26.5°C, provide the ideal environment for tropical cyclone formation. In fact, the ocean temperatures are 2-3°C above normal, even capable of sustaining a tropical cyclone off southeast Queensland.
Impact on Australia: The good news is that the likelihood of a tropical cyclone hitting the Australian region within the next 7 days is low. However, if one forms, it will likely remain distant from the mainland, posing minimal direct threats. But here's where it gets interesting: tropical cyclones generate massive waves that can travel vast distances. These long-range swells can affect Australia's coastline, even from thousands of kilometres away.
The upcoming event: Over the weekend, a low-pressure area near Fiji will intensify, possibly reaching tropical cyclone strength early next week. Although it will stay 2,000-2,500 kilometres east of Australia, the strong easterly trade winds around it will create significant swells directed towards the continent. These swells are expected to reach heights of 5 to 6 meters in parts of the southwest Pacific between Fiji and New Zealand.
The journey of the swells: The swells will take 3 to 4 days to travel the 2,000+ kilometres to the Australian mainland. While the swell height will decrease during this journey, the wave period will increase. This means that coastal areas in eastern Australia could experience the initial swells as early as Thursday afternoon, December 11, with periods of 14 to 15 seconds and small amplitudes.
The swell's impact: By Friday, December 12, the full force of the swell is anticipated to hit the coast, with waves reaching 1 to 1.5 meters at 12-second periods in certain areas. Some regions, like the NSW Northern Rivers and southeast Queensland, could see waves up to 2 meters.
Looking further ahead: Another tropical low might emerge south of the Solomon Islands mid-next week. While models predict a low developing in the northeast Coral Sea, there's uncertainty about its intensity and exact location. This potential cyclone could approach as close as 1,000-1,500 kilometres to northeast NSW and southeast Queensland by December 13, but its impact on swell generation will depend on its proximity, strength, and movement.
The danger of long-period easterly swells: These swells are particularly dangerous for Australia's east coast as they can bypass the usual defenses of headlands and breakwalls, which are designed to protect against south swells. The long-period groundswell energy can cause significant coastal erosion on beaches typically shielded from south swells. Moreover, this energy can create havoc in ports and harbors, causing ships to strain against their moorings and anchors, and seiching can further intensify this movement.
Stay informed: With this weather event approaching, it's essential for residents and visitors in eastern Australia to stay updated with the latest coastal warnings over the next two weeks. And this is the part most people miss—the potential impact of these swells on coastal infrastructure and marine activities. Are you prepared for the upcoming swell season? Share your thoughts and experiences in the comments below!
