Australia, keen geographers will tell you, isn't an island but a continent.

It might sit there totally surrounded by water, as islands do, but a continent it is, one that spans 35° of latitude, 40° of longitude, and measures 7.7 million km² of land.

This last week, however, Australia felt much more like an island when a single storm in the Southern Ocean provided swell to every surfable coastline of Australia.

Despite what you may have heard or read, this is a rare event. Occasionally a storm will intensify under Western Australia, then ease before flaring up again near Tasmania. But considering how it's staged, can that be considered a single storm?

Around the Swellnet office, we'd say no.

The swell that stopped the nation, however, was borne of a system that remained at storm-force intensity for 4,000kms, from a position southwest of Western Australia to south of Tasmania. It hit the Goldilocks zone for Australia-wide swells.

First forming last Wednesday, the 16th October, the storm deepened at a position roughly halfway between Heard Island and the southwest tip of Oz. Surface wind graphs (see below) show a large system sending south-southwest swell towards Australia.

Surface winds on Wednesday 16th October show the system developing below Western Australia

The swell struck WA's southwest on the morning of Friday the 18th, moving up the WA coast through the day. Our Yallingup surfcam recorded 6ft waves around midday (see image below), while Margaret River was much bigger near 8-10ft due to the acute direction. Mandurah was ridable but very small, owing to sheltering from the capes, same with Perth, while Kalbarri reached 4-5ft the following day.

Yallingup, Friday 18th October

In WA the swell was acutely south and short-lived. Through this phase of the storm, the bulk of the energy was directed further east.

A snapshot of the surface winds on Thursday the 17th show a very broad wind field, stretching from close to the ice shelf to the southern shore of Oz (see image below). The sheer expanse of wind helped direct energy into the various coastlines of South Oz, Victoria, and Tasmania.

Surface winds on Thursday the 17th

The swell hit South Australia's desert coast on Saturday peaking around 10ft, and by Sunday it had made its way up St Vincent's Gulf with the Mid Coast registering 2-3ft of swell (see surfcam image below), while around the other side of Kangaroo Island, Bullies on the Victor coast was 8ft.

Triggs on South Australia's Mid Coast, Sunday the 20th

Around the same time the swell struck South Australia, the forerunners were being felt further east in Vicco. By the morning of Sunday the 20th, the Surf Coast was around 6ft with larger surf to the east on the Mornington Peninsula and Phillip Island.

First light in Torquay, Sunday the 20th

To the south, Tasmania's West Coast felt the brunt of the swell with the Cape Sorell waverider buoy reaching 7m. Tasmania's South Arm beaches and up the east coast of the apple isle began to receive swell once the wind field moved east and elongated (see image below). And though the winds marginally reduced in strength, the sheer size of the fetch allowed the swell periods to stretch out.

Oddly, the South Arm coast came in below expectation, but 3-4 ft waves were reported in St Helens late Sunday and Monday.

Surface winds on Friday the 18th

Surface winds on Saturday the 19th and the last phase of the storm

Generally speaking, a storm that provided swell to Australia's west and south coasts would flare up southwest of West Oz, reach max size and intensity under WA, remain storm-force for approx 24 hours before receding in size and strength as it moved east.

In contrast, this system reached max size and intensity, then plateaued as it slowly moved east, changing shape but not its ability to generate significant swell. The image above is taken four days after the storm formed, and shows storm-force winds still blowing southwest across the Sothern Ocean, now rounding the southern coast of Tasmania.

Despite generating a southwest swell, the period moved towards the high teens allowing significant spread back towards Australia's East Coast. 

By Monday morning the swell was moving up the NSW south coast, with the Illawarra and Sydney region jumping to 4-5ft. The following surfcam image was taken at 11am at Shark Island, which is sheltered from pure south swell but nonetheless felt the approaching energy.

An hour or so later the NSW Central Coast was also feeling the effects, as seen by our Avoca cam.

The next day, Tuesday the 22nd October, was the best day of the season thus far for south swell magnets on the NSW coast with waves around 6ft all day. Some deepwater reefs amplified the long period energy with reports of 8ft sets coming in.

All this occured under a light northwest offshore, owing to a high pressure system parking itself over the East Coast.

In years gone by this would've been a classic mysto swell: it formed so far away, and was so 'off axis' for the East Coast, that very few people could've forecast it.

By Wednesday, the swell had filtered up the NSW coast with 3-4 ft waves reported on the Mid North Coast, 2-3 foot waves in Far Northern NSW, and a touch smaller on the Gold Coast. The broad high pressure system provided settled weather and morning offshores.

The image below is an auto screen grab from our Duranbah cam on Wednesday 22nd.

The swell ultimately reached the Sunny Coast, though as it was a southwest swell that travelled over 2,000kms rounding Tasmania, then Cape Byron, then Moreton Island, it was greatly attenuated, topping out around 2ft on Wednesday.

At least it was sunny.