Forecaster Blog: Long Enduring Run of South swell Brewing for the East Coast

29 May 2019 1 Share

Ben Macartney

Chief Surf Forecaster

Issued Wednesday, May 29, 2019

Following the long-lasting run of light winds, clear skies and long-range southerly groundswell across the Eastern Seaboard throughout the month of May, we’re finally witnessing the emergence of a new, early winter pattern; one that promises many days of sizeable South swell across the region under stronger cross-offshore winds. For the most part, the fluctuating swell will arriving under a fresh, WSW to SSW winds that will finally see the die-hard board-short wearers finally donning full-steamers – and it’s also looking like there will be plenty of opportunity to dust off your big-wave board.

Big, clean and cool. A deep, complex low delivers days of sizeable South swell to the East Coast, starting Thursday. Photo: Uploaded to CW by Mattypatek.

Big, clean and cool. A deep, complex low delivers days of sizeable South swell to the East Coast, starting Thursday. Photo: Uploaded to CW by Mattypatek.

The source of an impending increase in South swell into Thursday, Friday and the weekend is a large, complex area of low pressure that’s just setting up below Tasmania and the Tasman Sea; leading in the first major cold outbreak into the mid-latitudes for the autumn/ winter transition.

While this might look like a pretty typical, early winter south-swell, the specifics surrounding the storm’s influence on swell-production are quite unique. Already we’re seeing a first low pressure centre located over the Southern Ocean, some 2,400 kilometres south-southeast of Sydney, setting up a broad, severe gale force southerly fetch in conjunction with a large, stable high pressure over the Great Australian Bight. In its own right, this will generate a large pulse of southerly groundswell; arriving with a slight SSE bias at 12 to 14 second intervals later Friday through early Saturday.

A deep Southern Ocean low setting up some 2,400km's below the Tasman Sea sets up a first pulse of South groundswell over the next 24 hours. Source: Wave Tracker.

A deep Southern Ocean low setting up some 2,400km's below the Tasman Sea sets up a first pulse of South groundswell over the next 24 hours. Source: Wave Tracker.

However, it’s the development of a closer range SSW fetch linked to an embedded front passing southeast of Tasmania on Thursday and Friday that will add an additional southerly swell-train into the mix; this time exhibiting a straighter southerly bias at lower periods of 10 to 12 seconds into the mix.

An embedded frontal surge sweeping up below Tasmania on Thursday leads in a broader, closer range SSW fetch that will heavily compound wave-energy into Friday and the weekend. Source: BOM.

An embedded frontal surge sweeping up below Tasmania on Thursday leads in a broader, closer range SSW fetch that will heavily compound wave-energy into Friday and the weekend. Source: BOM.

Both of these swells will blend into one, very energetic swell-train to arrive in tandem; generating a pretty dramatic increase in wave heights across Sydney and surrounds throughout Friday afternoon and into Saturday, ahead of a corresponding increase following across mid-northern NSW and southern Queensland coasts over the course of the weekend.

While the combined effects of the dual swell-source will no doubt result in plenty of size in the 6 to 8ft range through the height of this event, it’s also notable for the resulting, high spectral density of the swell: characterised by a much broader spread in wave-height and periodicity. In short, that will mean consistent surf making for challenging, if not chaotic conditions across the more exposed south-facing stretches – and this will lend the focus to sheltered southern corners and more north-facing breaks under prevailing West  to south-westerly, tending SSW winds.

The swell should progressively scale back in size throughout Sunday, but it’s becoming increasingly clear we’re in for yet another, very large increase in South to SSE swell early to mid next week; linked to a deep mid-latitude low developing over the southern Tasman Sea. Details on this event will become clearer as the models gradually get a better handle on its development, so stay tuned for updates later in the week.


The evolution of a deep Tasman low early next week hints at yet another large S to SSE swell event unfolding into the first week of June. Source: Wave Tracker.

The evolution of a deep Tasman low early next week hints at yet another large S to SSE swell event unfolding into the first week of June. Source: Wave Tracker.


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