Australia’s East Coast could be impacted by periods of strong waves over the next couple of weeks as tropical cyclone activity increases in the Coral Sea and southwest Pacific Ocean.

A number of these computer models are forecasting the development of tropical lows or cyclones over the Coral Sea and southwest Pacific over the next two weeks.

Image: Four computer models predicting tropical lows or cyclones being active east of Australia late next week. Source: Weatherzone.

This increased potential for tropical systems in the region is partly driven by an active phase of the Madden-Julian Oscillation (MJO) moving into the western Pacific region. The MJO causes an increase in cloud and thunderstorm activity when active over a region. This enhanced storminess can help create low pressure systems that can deepen into tropical cyclones.

Image: Conceptual visualization of the MJO moving over the north of Australia, increasing thunderstorm, rain and tropical low activity. Source: Weatherzone.

Along with this active phase of the MJO, oceans are very warm across the Coral Sea and southwest Pacific. This is partly due to the weak La Niña conditions currently in place across the Pacific.

These warm sea surface temperatures greatly increase the potential for tropical cyclone development, which requires waters warmer than 26.5°C. Currently oceans across the region are 2-3°C warmer than normal, with waters even warm enough to support a tropical cyclone off southeast Queensland.

Image: Sea surface temperatures around Australia on Thursday, December 4, 2025. Source: DTN.

How will Australia be impacted?

Fortunately for those in eastern Australian, there is only a low chance of a tropical cyclone being within the Australian region in the next 7 days.

If a tropical cyclone does form, it will most likely be located a long way off Australia’s east coast and pose very little direct threat to the Australian mainland. However, tropical cyclones generate very large seas that radiate across the oceans, and these long-range swells can impact Australia’s coastline from thousands of kilometres away.

Over the weekend, an area of low pressure will deepen near or just south of Fiji, potentially briefly reaching tropical cyclone intensity early next week before undergoing extra-tropical transition. While this system will remain around 2,000-2,500 kilometres east of Australia, enhanced easterly trade winds around the low, with more powerful 35-45 knots winds near the core, will generate a large area of swell generation, directed towards Australia.

Image: DTN’s OneFX Significant Wave Heights reaching 5 to 6 m generated on Tuesday, December 9, 2025. Source: Weatherzone.

Large seas generated by the low should reach 5 to 6 m over parts of the southwest Pacific between Fiji and New Zealand early next week. This area of large waves being over 2,000 kilometres away from Australia’s East Coast will take about 3 to 4 days to propagate and reach the Australian mainland. Across this journey, the swell height will significantly decrease, but the wave period will increase.

Image: DTN’s OneFX Peak Wave Period showing easterly swell propagating across the Tasman and lower Coral seas next week. Source: Weatherzone

In deep open ocean waters, longer period swell travels faster than short period swell, so coastal parts of eastern Australia could see swell “front runners” as early as Thursday afternoon (December 11). These swell propagation leaders should come in with periods of 14 to 15 seconds, and small amplitudes of less than a metre.

The bulk of the swell energy is then expected to fill into Friday, December 12, with coasts from the NSW South Coast to Queensland’s K’gari experiencing 1 to 1.5 m swell at 12 second periods, and up to 2 m around the NSW Northern Rivers and southeast Queensland.

Looking further ahead, another tropical low could develop just south of the Solomon Islands from mid-next week. While most models feature a low developing in the far northeast of the Coral Sea next week, different model and model runs vary on the intensity and location of the system.

Image: GFS weather forecast of Mean Sea Level Pressure (MSLP) and 10 m wind speeds between Sunday, December 7, 2025, and Thursday, December 18, 2025. Source: TropicalTidbits.com

This possible tropical cyclone could come within 1,000-1,500 kilometres of northeast NSW and southeast Queensland from around Saturday, December 13. The potential for significant easterly swell generation will greatly depend on the proximity, intensity and movement of the system.

Why long period easterly swell can be dangerous and disruptive

Easterly swells are especially hazardous for Austarlia’s east coast because they can bypass the headlands and breakwalls that protect beaches, ports and harbours from the more typical south swells that impact NSW and southeast Queensland. These easterly swells can enhance coastal erosion across beaches usually protected from south swells.

Long period “groundswell” energy often goes unnoticed underneath ships at sea, but can be highly disruptive as the energy surges into ports and harbours. The “waves” of deep water energy surging into ports can cause ships to drag on their moorings and anchors. Seiching can also amplify this water movement as the energy sloshes within the port boundaries, increasing horizontal and vertical ship movements.

Be sure to check the latest coastal warnings in eastern Australia over the next two weeks before heading down to the beach.