Southern Ocean Swell Alert: Thursday, April 16, 2015

16 Apr 2015 0 Share

Ben Macartney

Chief Surf Forecaster

Issued Tuesday April 16, 2015

While Western Australian coasts have benefited from a sustained run of SW groundswell that’s set to continue over the next few days, the final stages in the lifecycle of the intense Southern Ocean low responsible for the swell occur deep below the Australian mainland over the next 24 hours – giving rise to a large SW groundswell across southern Australia states this weekend.

Victoria's Surf Coast is likely to be one of the few places making sense of the groundswell as it peaks this weekend. Photo: Judy Scanlon.

Victoria's Surf Coast is likely to be one of the few places making sense of the groundswell as it peaks this weekend. Photo: Judy Scanlon.

  • An extratropical low over the far south-eastern Indian Ocean is forecast to intensify and migrate below Western Australia over the next hours.
  • As the low strengthens it supports an extensive gale to storm force WSW fetch below the continent, driving significant wave heights to peaks of 40 to 50ft over the Southern Ocean on Friday.
  • A long period SW groundswell emanating from this source travels northeast to impact South Australian and Victorian Coasts this weekend.
  • The leading edge of the groundswell should build steeply across all regions throughout Saturday afternoon ahead of the bulk of swell peaking on Sunday morning.

Overview
The evolution of a complex extratropical low over the Southern Ocean now holds definitive potential for a large-scale pulse of SW groundswell across Victorian and South Australian coasts this weekend. Although recent model runs have downgraded the size of the swell ever so slightly, the various computer models have generally remained consistent in their projections all week and there’s little doubt this event will produce extra-large surf across the entire southern Australian coastline – particularly as the swell peaks on Sunday morning. Although the passage of a deep low pressure system below Western Australia Over the next 24 hours is the key driver of significant wave heights to peaks of 40 to 50ft over the Southern, this is just the final stage in a period of heightened storm-activity linked to the passage of a long-wave trough through the eastern Indian Ocean this week.

Indeed this episode is the culmination of a complex low pressure system migrating deep below Indonesia this week, featuring consecutive storm-systems leapfrogging one another to drive deepwater swell to increasingly larger levels with the passage of each low. So as mentioned the final stage of this heightened storm activity occurs directly below the Great Australian Bight on Friday before the low begins to weaken – at which point the 40 to 50ft deepwater swell will be roughly 900 nautical miles southwest of Bass Strait. A long-interval SW groundswell will take the best part of Friday and Saturday to cover this distance before beginning to make landfall across Victorian and South Australian coasts; building steeply towards dark on Saturday ahead of a peak in size early on Sunday.

The deep, 970 hPa low southwest of WA drives deepwater swell to peaks of 40 to 50ft as it traverses deep below the continent on Friday. Source: BOM.

The deep, 970 hPa low southwest of WA drives deepwater swell to peaks of 40 to 50ft as it traverses deep below the continent on Friday. Source: BOM.

Latest Wave Tracker model runs pick up 40ft+ deepwater wave heights over the Southern Ocean on Friday.

Latest Wave Tracker model runs pick up 40ft+ deepwater wave heights over the Southern Ocean on Friday.

This should produce surf heights ranging from 4 to 8ft across South Australia’s South Coast beaches, while producing significantly larger surf across the state’s more exposed stretches of coastline. Likewise Victoria’s exposed beaches will receive a heavy push in surf ranging from 8 to 12ft plus depending on the exact location, but strong onshore SSW winds will invariably leave these regions entirely deserted. The one region likely to be handling the swell will be the premier breaks of Bells Beach and Winki Pop located along Victoria’s Surf Coast. These breaks are likely to see a solid 6 to 8ft day with the odd 10ft bomb a distinct possibility early on Sunday. The downside is a gusty SSW wind-shift following the passage of an associated cold front across Bass Strait on Saturday night. While there’s a possibility early inshore W winds will see a window of clean conditions at these breaks, it’s likely to swiftly come to a close as the SSW flow kicks in during the morning.

For more details on the Victorian forecast click here.

For more detalls on the South Australian forecast click here.

The Wave Tracker's nearshore modelling for Victoria depicts the peak of the swell pushing into western Bass Strait in the 20ft range before wrapping in along the Surf Coast early on Sunday morning.

The Wave Tracker's nearshore modelling for Victoria depicts the peak of the swell pushing into western Bass Strait in the 20ft range before wrapping in along the Surf Coast early on Sunday morning.

Latest virtual buoy readings for Torquay show the bulk of the SW groundswell arriving on Sunday morning at peak wave periods of 16 to 18 seconds.

Latest virtual buoy readings for Torquay show the bulk of the SW groundswell arriving on Sunday morning at peak wave periods of 16 to 18 seconds.


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