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East Coast Low to bring flooding rain, gales, huge waves to eastern NSW

Warnings for strong to gale force winds, hazardous surf and flooding are in place across eastern NSW and southeast Queensland as an East Coast Low develops.

A deepening coastal trough over southeast Queensland and northeast NSW has already brought widespread falls of 30 to 70mm over Sunday afternoon and Monday morning. Dunwich Airport, on North Stradbroke Island, Queensland, collected 103mm in the 24 hours to 9am.

Image: Satellite imagery showing a coastal trough across eastern Australia between Sunday, June 29, and Monday, June 30, 2025.

Explosive cyclogenesis to spawn East Coast Low

The coastal trough currently positioned off the NSW’s Northern Rivers will rapidly intensify through a process of explosive cyclogenesis.

This explosive process means that the central pressure of the system is expected to drop rapidly from about 1015 hPa around midday on Monday, to about 993 hPa 24 hours later on Tuesday. The drop of over 20 hPa in 24 hours classifies the system as a bombing low, exceeding the required 15 hPa drop at this latitude.

Video: forecast Mean Sea Level Pressure (MSLP) and 6-hour rainfall between Monday, June 30 and Sunday, July 6, 2025.

As mentioned in our previous article on what makes an East Coast Low, this rapid intensification comes as a result of a number of factors, including:

1. Warm Sea Surface Temperatures (SST)
2. Baroclinic instability (a large termperature difference in air masses)
3. A blocking high pressure system
4. An upper trough over the Great Dividing Range

Where will be most affected and when?

As the ECL develops over the coming 24 hours, moisture wrapping around the low will shift southwards.

As seen in the image below, most weather models focus the heaviest rainfall around the Mid North Coast and parts of the Hunter, with150-200mm over a period of 24-36 hours to early Wednesday. Winds will also intensify overnight into Tuesday, most likely south of Coffs Harbour.

Image: MSLP and 24-hour rainfall accumulation at 1pm on Tuesday, July 1, 2025, according to ECMWF (top left), GFS (top right), UKMO (bottom left) and ACCESS-G (bottom right).

East Coast Low reaches peak intensity

From midday on Tuesday, extending into Wednesday, the ECL is expected to reach its peak intensity in close proximity to the coast with the central pressure expected to drop to around 980 to 985 hPa.

Much of coastal NSW between Batemans Bay and Port Macquarie is at risk of experiencing wind gusts exceeding 100km/h on Wednesday morning, with areas on and east of the Great Dividing Range also experiencing strong winds.

Image: Forecast 10 metre wind gusts at 10am on Wednesday, July 2, 2025.

Flooding rainfall reaches Sydney and Illawarra

Intense heavy rainfall will shift southwards into the Sydney and Illawarra regions from about midday on Tuesday, reaching its peak intensity overnight into Wednesday morning. Another burst of moisture and rainfall will sweep over southeastern NSW between Wednesday afternoon and Thursday morning as an arm of the ECL moves inland.

Across the coming 48-60 hours, widespread falls of 150-250mm are expected south of about Port Macquarie, with more intense deluges of 300-400mm possible across parts of the Illawarra and Shoalhaven regions between Monday and Thursday evening.

Image: Rainfall accumulations across NSW to 10pm on Thursday, July 3, 2025, according to ECMWF (top left), GFS (top right), UKMO (bottom left) and ACCESS-G (bottom right).

Powerful and hazardous surf

Along with the rain, the powerful winds wrapping around the ECL will generate large and hazardous surf, likely leading to significant erosion in some areas of coastal NSW.

Significant wave heights of 5 to 6 metres are expected across coasts between Seal Rocks and Batemans Bay, with large waves extending further south and north. Maximum wave heights of 11 to 13 metres are also expected over a similar region.

Image: OneFX forecast Significant Wave Heights at 10am on Wednesday, July 2, 2025.

Wave energy coming from the east will significantly enhance coastal erosion, especially across parts of the Central Coast, Sydney and Illawarra which are more exposed to most of this energy. Fortunately, the high tides next week will only be moderate in height with the neap tide occurring later in the week.

Image: Erosion prone beaches, like Narrabeen-Collaroy Beach, are in a vulnerable state ahead of this week's swell. Source: Felix Levesque.

When will the weather clear?

The East Coast Low is expected to move east further into the Tasman Sea on Thursday afternoon, with heavy rain and strong winds gradually easing as it does so. By late on Thursday, or early on Friday, most of the rain should be offshore, with winds abating as well. The swell is expected to remain large into Friday, but should ease significantly into the weekend.

Keep up to date with the latest warnings and our news feed for updates on the Weatherzone warnings page.