Queensland surfers of a certain age will recall the famous 28 day swell of 1975 - or was it a 24 day swell? Whatever the time frame, the myth goes that a trade wind belt parked itself under New Caledonia and blew strong easterlies at the Gold Coast, and kept blowing them until Gold Coast surfers couldn't paddle anymore.

It's not quite a case of history repeating but a recent weather event did something similar.

From just before the Easter weekend right through until the weekend just gone, the East Coast saw persistent levels of easterly groundswell. From Agnes Waters down to Ulladulla and beyond set waves hovered between 3ft, with bigger 4ft bombs in the mix, spaced 10-15 minutes apart.

Already a rare event, the swell coincided with an unusually long run of light winds, creating great conditions on most days, even fending off afternoon seabreezes providing full days of glassy surf.

However, if during the course of the swell you checked the usual synoptic charts you'd have been baffled to pinpoint the swell's source. Tropical Cyclone Cook produced a short-lived NE groundswell prior to Easter yet it vanished off the charts as quickly as it came.

Likewise, the usual trade wind belt below New Caledonia, the source of the legendary 28 day swell, was quiet. Where was this mystery swell coming from?

The source of this swell was well past New Zealand, way out and south of Tahiti. Over 4,000 kilometres away - which explains the wait between sets. The swell was a product of a stationary flat-topped high working in tandem with a tropical low to generate a fetch of easterly gales aimed towards the Australian East Coast. These swells are unique in that the ocean reaches a "fully formed sea state" producing a unifom organised swell signature.

So from Monday the 10th of April through to Thursday the 20th - when the system drifted north-east and started to break down - we saw a steady supply of easterly groundswell generated for New Zealand and Australia.

The swell lit up an A-grade rivermouth across New Zealand's North Island for six days straight, arriving across the Australian East Coast Easter Saturday and persisting for over a week while ever so slowly dropping in size.

It wasn't only the longevity that was unique but its positioning too. The fetch was created just far enough north of New Zealand for southern NSW to also receive swell. If the system was any further south the North Island would create a swell shadow that only SE Qld and northern NSW would escape.

Besides the inconsistency of the swell, another downfall was its uniformity, though this comes with a caveat. If you didn't have a top quality sand bank, reef, or pointbreak at your disposal, the swell created bank to bank closeouts.

Over the last few days another strong easterly groundswell has impacted the East Coast, but this was from a separate low pressure system forming just north of New Zealand once the original broke down. So our best guess is the distant storm created swell for 10 days, which is awfully rare for the East Coast.

The next question, of course, refers to the famous 28 day swell: Was it the product of a lone system or a chain of systems?

We'll leave that to the old blokes - maybe something to debate over a beer? - as the rest of us hook into the late autumn swell.

//CRAIG BROKENSHA & STU NETTLE