For the past couple of weeks, it’s been generally quiet on the eastern front, with all the swell activity being focussed up into Western and South Australia. However, this is all set to change this weekend with an extended run of large surf from the east expected.

Though eyes are usually trained to the south, mid-winter east swells aren't uncommon. What is unexpected is the longevity of the coming swell.

At present, the northern half of the NSW coast is staring down the barrel of at least four days of large surf, likely starting windy and extra-large before organising itself and wagging a very long tail.

Backlit winter perfection (Brokensha)

The source of the swell will be an upper level trough currently moving across the country, which spawned off the strong cold outbreak that impacted Western Australia yesterday.

The high level instability will move across the continent before crossing the East Coast over the weekend, while an additional injection of polar air from the south will help provide the catalyst for the development of a broad low pressure system offshore from the Mid North Coast sometime on Saturday.

Another unexpected aspect of this storm will be the formation of multiple embedded lows around a broad centre, with multiple fetches of gale to severe-gale-force winds being projected on top of an established fetch of strong easterly winds - see image below.

This and the slow eastward movement away from the coast will create initially windy, raw XL surf, though as the low starts migrating away from the coast, westerly offshore winds are expected to kick in as the low continues to generate large surf.

Approaching frontal activity through the Bight and across the south-east of the country should bring favorable winds for nearly all next week with the low still generating swell into the following weekend as it broadens into a substantial trade-fetch north of New Zealand later next week.

There’s even the chance for a repeat, though much weaker, system into the following week, but that’s getting way too far ahead of ourselves.

Looking at the specifics and we’re due to see increasing rain and strengthening onshore winds as the low forms on Saturday, becoming larger through Sunday and likely reaching the XL size range later in the day, if not more so Monday.

The timing of the offshore change looks to be later Monday, with the surf up until then being mostly a write-off apart from novelty spots and locations north of the lows axis.

Tuesday onwards looks great as offshore winds kick in and the swell starts to become more manageable for a wider variety of locations.

At present, the leading global forecasting models ECMWF (European) and GFS (American) are fairly similar in make-up and evolution of this coming system but we’ll provide running updates in the commentary below while the regional Forecaster Notes will have more precise details as the weekend nears closer.

// CRAIG BROKENSHA