Seasonal swing: Two swells that signify the changing seasons

Stu Nettle picture
Stu Nettle (stunet)
Swellnet Analysis

There are many disadvantages to being an east coast surfer: protracted flat spells, unpredictable weather systems, and half-day wonder swells are just a few of the more frustrating problems. However, despite the many drawbacks there's also an advantage to living on the right coast and recently it came to the fore. During the last month we had two swells that contrasted heavily in nature and highlighted the advantage of having a swell window that opens a full 180 degrees.

The two swells couldn't have been more different. The first event was in mid-March, an E/NE swell that formed when Tropical Cyclone Lusi drifted south-east of Fiji to be cradled by a high pressure system. The pressure gradient it created sat above that special slice of ocean north of New Zealand. The swell arrived long-lined and uniform in nature, drawn out to an impressive 15 second+ period. It also travelled far from the source and arrived under completely different climactic conditions then those it was created. When the swell made landfall the weather in Sydney and the southern NSW coast was close to perfect, a mild early Autumn day with offshore wind from sunrise to sunset.

The second swell, which hit on the weekend just gone, contrasted markedly. It was the byproduct of an intense Tasman low pressure system that formed off the NSW South Coast late on Friday. The low deepened rapidly into Saturday morning, driving a broad fetch of southerly gales parallel to the southern NSW coast. The swell they created was 180 degrees due south, also running parallel to the coast. As is typical of these swells it was close-range – the waves broke barely 500kms from where they were formed. And the wind that formed those waves also impacted the entire southern NSW coast. The best waves broke in the lee of headlands sheltered from those winds.

If we're to look for seasonal manifestations of swells then the above two events speak for summer and winter. The TC Lusi swell was a classic Summer swell: driven by warm air and water, tropical instability, and a merging with the trade wind belt. The most recent swell a quintessential East Coast Winter swell, bringing violent winds and highly directional south swell.

By chance they peaked exactly a month apart – to the day. Coincidental timing aside, what the two swells signalled was the changing of the season on the East Coast, the slowing of our northern swell window as the southern swell window starts kicking into life.