Generally poor weekend, better next week

Craig Brokensha picture
Craig Brokensha (Craig)

Western Australia Surf Forecast by Craig Brokensha (issued Friday May 21st)

Best Days: Perth and Mandurah Sunday morning, protected spots Monday, Tuesday, Wednesday selected spots

Features of the Forecast (tl;dr)

  • Mod-large, mid-period W/SW swell for tomorrow with strengthening NW tending W winds ahead of a late S change
  • Easing swell Sun with stronger onshore winds in the South West, variable to the north in the AM
  • Oversized, long-period SW groundswell for Mon with strong S/SW winds, easing slowly Tue with light, offshore, variable winds
  • Smaller Wed with freshening E/NE tending NE and then N/NE winds


The surf cleaned up nicely yesterday along with Wednesday afternoon's swell hanging in there, coming in at 5-6ft across the South West, 2ft+ in Mandurah and 2ft across Perth.

This morning conditions were again clean but the surf smaller and on the ease.

This weekend and next week (May 22 - 28)

We'll see the surf pick right back up tomorrow, but unfortunately it'll come with onshore winds as a weakening trough linked to the swell generating system moves through.

We'll see a strengthening NW tending W'ly breeze in the South West, similar to the north but only swinging W'ly early afternoon along with all coasts swinging S'ly into the evening.

The swell due across the state was generated by a tight mid-latitude low earlier this week and we should see the South West come in around 6ft+ through the day, 2-3ft in Mandurah and 2ft across Perth.

Sunday should become cleaner across Perth and Mandurah with an E/SE offshore wind, tending variable ahead of a SW change early afternoon. Size wise the swell will ease a touch back to 2ft+ in Mandurah and 2ft across Perth while Margs will see poor conditions with a moderate to fresh SW breeze, strengthening through the day.

This strengthening onshore wind will be associated with the strong polar low that's currently just south-east of the Heard Island region, projecting up and into us, with our oversized SW groundswell mixed with mid-period energy still on track for Monday.

A fetch of storm-force W/SW winds are currently being generated with the low tracking east-northeast and the north-east up towards us while slowly weakening tomorrow. We'll then see strong S/SW winds projected into the coast through Monday adding the mid-period energy to the mix.

Size wise the South West should still reach 12ft with 15ft bombs due across the deepwater reefs and magnets, with Mandurah coming in around 4-5ft+ with the mix of windswelly stuff, 3-4ft in Perth.

Those strong S/SW winds will create poor conditions though, improving through Tuesday as winds shift light E/SE across all locations in the morning, possibly E/NE through the middle of the day and variable into the afternoon.

The oversized mix of swells should be on the ease, dropping from an easy 10ft across the South West in the morning, 3-4ft across Mandurah and 3ft in Perth.

Wednesday will be smaller and with moderate to fresh E/NE tending NE and then N/NE winds as a strong mid-latitude low starts to move in from the west.

The low will be slow moving and bring N'lyn winds into the end of the week along with an inconsistent, long-range SW groundswell with no major size, while some new swell from the mid-latitude low itself is due on the weekend. More on this Monday though. Have a great weekend!


bluediamond's picture
bluediamond's picture
bluediamond Friday, 21 May 2021 at 4:34pm

Great thorough report. Thanks Craig..
Just a quick question if you have time.
The hardest thing for me to work out is the speed these swells travel across such vast oceans and their arrival times. I do recall seeing an equation for period which calculated that?
And does the storm that created this swell run a little ahead of the actual main swell energy, or is the swell preceeding it slightly. Going by the forecast models, it looks like the winds arrive first. It's such a huge ocean, looking at a map you lose scale of how far these swells have to travel. Cheers.

trevbucky's picture
trevbucky's picture
trevbucky Friday, 21 May 2021 at 11:49pm

Hey Blue, I’m no expert like Craig, but from what I’ve learnt it’s different in every case.

Often the big ground swells from deep in the Indian Ocean will peak way out near Heard Island and send a swell thousands of kilometres towards us. Obviously the stronger the storm the bigger the swell. The further away it peaks, and the bigger it is, the longer the period.

Sometimes (actually quite often) the swell arrives before the storm. Add in some offshore winds near the coast and the more lined up and “corduroy” it can become before we get it. This is when we get those classic days with groundswell & offshores.

Then the storm that generated it passes by which can bump up the swell again. Too high (like in late Autumn/Winter/ early Spring) its onshore & junky (even if it goes offshore the next day), but if it passes us low, we’ll get SE winds & a nice clean kick in SSW swell.

bluediamond's picture
bluediamond's picture
bluediamond Saturday, 22 May 2021 at 9:02am

Hey cheers TB. Yeah looks like this storm really revved up initially down off Antartica but slowly lost intensity as it powered NE towards us. It's moving pretty fast relative to wave movement away from it, maybe overtaking it. So i guess that's why the slower moving systems and fetch create bigger more powerful surf,(not that 8m isn't big but can get alot bigger down here occasionally) because the winds don't overtake the swells creating deterioration? Maybe. haha. The perfect storm! Some great insight there. Thanks mate.

trevbucky's picture
trevbucky's picture
trevbucky Saturday, 29 May 2021 at 2:48pm

No worries blue, that’s exactly right a nice powerful slow moving storm that stays low (and a high pressure system over WA) is the ideal system to produce a long period clean groundswell.

That’s why the lucky buggers on the far north coast & Qld coast get epic waves for a week or so from a cyclone just sitting off in the coral sea!