Southern Ocean Swell Alert: Tuesday, 28 July 2015

28 Jul 2015 1 Share

Swell Alert Issued 28 July 2015. By Ben Macartney and Matt McKay.

Wrapping yourself head to toe in a good half centimetre of rubber and taking on exceptionally large Southern Ocean groundswell in water temps in the low teens isn’t every surfers cup of tea. Still, wetsuits have come a long way and if you are of the hell-man ilk, then the following may be of interest. Both the Victorian and South Australian coasts are set to overachieve in the surf department during the opening days of August as a major activation of the Southern Ocean storm track delivers a succession of large SW groundswells to the region.

Victoria's Surf Coast is likely to see an extended run of large SW groundswell under westerly winds, commencing this weekend and enduring through early to mid next week. Photo: Judith Scanlon.

Victoria's Surf Coast is likely to see an extended run of large SW groundswell under westerly winds, commencing this weekend and enduring through early to mid next week. Photo: Judith Scanlon.

  • A succession of deep low pressure systems migrating below the Australian mainland from Thursday onwards aim a series of large SW groundswells at South Australian and Victorian coasts over the weekend and early next week.
  • A first SW groundswell building in this weekend is forecast to produce heavy surf ranging from 8 to 10ft or more across exposed coasts.
  • A second, phenomenal pulse slated to fill in on Monday is projected to exhibit a deepwater peak in the 10-metre range.
  • Victoria’s Surf Coast will be a primary beneficiary from both pulses; receiving an extended run of large surf under a predominant westerly airflow.
  • Recent long range computer modelling hints at a third and final pulse of SSW groundswell arriving around Wednesday 5/ Thursday 6 August.
  • As the storm-track migrates further east below Tasmania over the course of next week it will extend strong S swell along the Eastern Seaboard and also direct large SW groundswell at New Zealand and Fiji.

Overview
In the wake of a subdued phase in winter storm activity through Australian longitudes through most of July we’re now on the cusp of a major reactivation of the Southern Ocean storm-track. A succession of deep low pressure systems developing under Western Australia are forecast to intensify as they migrate below the mainland from Thursday onwards – in turn giving rise to a series of large SW groundswells for southern Australian coasts. This upswing in activity is linked to a strong surge in the long-wave trough through Australian longitudes and it’s set to manifest as a large low-pressure complex anchoring over the Southern Ocean below Victoria and Tasmania this weekend. Although at this early stage there’s still enough divergence among the key computer models lending some uncertainty to the size and timing, there’s little doubt both Victoria and South Australia will feel the brunt of two or three large SW groundswells over the weekend and early next week.

This activity commences with a first low intensifying over the southeast Indian Ocean on Wednesday before intensifying below Western Australia on Thursday. As this deep polar low begins its eastward journey below Australia on Friday a large fetch of gale force winds aims a strong mix of, mid and long period SW groundswell at the Australian coastline. This slow moving system will begin to affect the South Australian coast late Friday/ early Saturday, with wave heights jumping dramatically in the wake of an associated cold front clipping the region no Friday night. By Sunday morning wave heights are expected to ease a touch before being reinforced again in the late afternoon/ evening. The body of this fetch is projected to carry northeast, towards Bass Strait as it gradually weakens throughout Friday, driving SW swell to deepwater peaks of 20 to 30ft below the Bight on Saturday morning. This should translate into a strong building trend in surf heights across Victoria throughout Saturday, with first peak likely to occur on Sunday.

FOR A DETAILED SURF FORECAST FOR SOUTH AUSTRALIA CLICK HERE

Although this first low isn’t looking exceptional with respect to wind-strength, duration – and hence swell potential, it’s a second anteceding frontal progression forecast to intensify along the same storm track on Friday and Saturday that does hold phenomenal swell-potential for the region. This low is anticipated to deepen significantly as it moves beneath Victoria, with current GFS model guidance capturing a large area of storm force winds (45-50knots) within this system. This vast fetch is likely to undergo a third resurgence as an embedded front tracks northeast below the Bight on Sunday. This fetch piggybacks on the still highly active sea-state leftover from the first low to produce significant offshore wave heights in excess of 35 feet. At this stage, a subsequent SW groundswell is expected to peak both across South Australia and Victorian coasts on Monday, with scope for peak size to spill over into Tuesday morning.

FOR A DETAILED SURF FORECAST FOR VICTORIA CLICK HERE

The primary region benefiting from this activity is Victoria’s Surf Coast. The region is anticipated to benefit from favourable WNW winds as the first pulse builds in, producing a full weekend of excellent surf ranging from 5 to 8ft. At this stage the second, heavier push in SW groundswell arriving early next week holds potential for chunkier sets peaking in the 8 to 10ft plus range. This is set to coincide with strengthening W winds, with a strong SW change likely to coincide with Monday’s peak size. Again, the timing and size of this episode will become clearer as the storm-system develops over the next few days, so stay tuned to the forecast for further updates as the week progresses.

FOLLOW THE PROGRESSION OF THE SWELL ON THE WAVETRACKER

This image depicts GFS model forecast surface wind for Friday night, showing the first and second swell sources lining up with Victoria and South Australia.

This image depicts GFS model forecast surface wind for Friday night, showing the first and second swell sources lining up with Victoria and South Australia.

This Wave Tracker image depicts significant wave heights for Sunday 2 August. The passage of the second low is projected to drive deepwater SW swell to heights of 10 metres over the Southern Ocean - in turn setting up a heavy spike in SW groundswell for Victoria and South Aus on Monday.

This Wave Tracker image depicts significant wave heights for Sunday 2 August. The passage of the second low is projected to drive deepwater SW swell to heights of 10 metres over the Southern Ocean - in turn setting up a heavy spike in SW groundswell for Victoria and South Aus on Monday.


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