Shades of Black
A fortnight ago I posted an analysis article on the peculiar early winter weather systems surrounding the continent. In the article, I made a prediction on the coming fortnight of surf, noting that we'd passed the winter solstice and the typical frontal systems were yet to be seen in the Southern Ocean, while the short term outlook continued this trend.
Meanwhile, the charts were hinting at an out-of-season synoptic setup off the East Coast, supplying a run of sizable swell out of the east.
From 22nd June:
“Similar to other setups we've already seen this year, easterly trades extending out into the western Pacific Ocean should produce a prolonged easterly swell event from late next week, into the following week, biggest across south-east Queensland and northern NSW, grading smaller further south.”
While the models swayed back and forward as the event neared closer, what initially looked to be just a strong low tucked in behind the shadow of New Zealand, started to transform into a setup that would favour all locations from Queensland to Tasmania's east coast.
Most east swells of note are products of the trade wind belt, which fluctuates in strength through summer and autumn. While forecast to arrive from the same direction, this swell had an entirely different synoptic setup. And while it was rare, it wasn't entirely unheard of, though it'd been five years since we'd seen a swell created from a similar event.
Winding back to June 2016, the Black Nor'Easter storm and swell event brought huge ridable waves to the East Coast.
The catalyst for that event was a deep infeed of east-northeast winds spanning from Fiji to almost the East Coast, being gradually squeezed by a deepening zipper-like trough line running along the coast. This saw north-east winds gradually strengthen on top an active and expansive sea state, with embedded lows producing stronger burst of gale-force winds.
The swell rose rapidly and once the trough moved offshore, winds swung, cleaning up large, ruler-edged 15ft sets - occasionally even bigger - during the first day of the swell, the size then tapering through the week.
The setup responsible for the current swell is very similar in structure, though not quite as strong as the July 2016 version. Also, the 'zipper line' of troughs sat further offshore, more towards the central Tasman Sea, which reduced the fetch and subsequent size impact.
The longevity of the current swell is due to the strength of the high pressure system sitting over New Zealand, registering 1040hPa, which, at that latitude, is usually only seen in summer. Combined with the cut-off low sitting further east in the South Pacific Ocean (see image below) and the zipper line to west, the high was being squeezed on both sides while seemingly held in place.
Just as the high pressure system is inching eastward, so too is the trough line. It's very slowly pushing the whole swell-generating setup further towards New Zealand, and this is the key to the longevity and quality of the swell event. While at times it overpowered some beachbreaks, it's been mostly accessible with pumping surf in the six foot range across southern NSW, bigger in select areas of northern NSW and south-east Queensland.
This satellite loop from yesterday shows the trough line (cloud east of it and clear to the west) and an embedded low pushing slowly east, towards New Zealand as the sun sets from the east.
I've posted a gallery from various sessions across the Sydney region here, but below are a few B-sides that didn't make the top twenty cut.