Impressive long period swells inbound

Western Australia Surf Forecast by Ben Matson (issued Saturday 17th October)

Best Days: Mon/Tues/Wed/Thurs: pulsey long period swells with good winds Tues/Thurs mornings. Most size expected Wed, though conditions are likely to become wind affected. 

Recap: Building swells across the Margs region on Thursday became wind affected throughout the day and were best on Friday morning with early light offshore winds, and size around the 3-5ft mark. It’s dropped right back today to a slow 2-3ft tops. The swell direction hasn’t been favourable for Perth and Mandurah coasts unfortunately.

This weekend (Oct 17 - 18)

*This week’s Forecaster Notes will be a little erratic as Craig’s on annual leave*

No change to the weekend outlook at all, with no new swells on the way.

Light morning winds and sea breezes are expected both days, and wave heights will remain very small across the Margs coast, with inconsistent 2ft, rarely 2-3ft sets at the swell magnets. 

Expect a continuation of tiny surf across the Perth and Mandurah coasts, only suitable for beginners. 

Next week (Oct 19 onwards)

A series of powerful Southern Ocean lows in our far swell window have generated (and are still generating) excellent long period swells that will arrive in succession from Sunday evening onwards (leading edges on Sun/Tues night could be around 20+ seconds).

The latest model guidance has strengthened these systems a little more since Wednesday and also maintained their strength a little closer to the mainland, which will assist in maximising surf size potential throughout Western Australian waters. The second swell in particular looks to be the biggest of the two, though will be sourced from a more eastern position in our swell window, so the resulting swell direction will be more SW thru’ S/SW.

However, the large travel distance will result in very inconsistent set waves. This will be most prominent on Monday and Tuesday, when the first groundswell will essentially be the only swell source in the water. On Wednesday and Thursday, the second long period groundswell will sit on top of decaying energy from the previous swell event, which (despite being smaller in size) will help to reduce the perceived inconsistency a little.

So, how big? At this stage I think we’ll see Monday building to 6ft+ across the Margaret River swell magnets during the day, possibly undersized early morning (expect flat spells of up to 15-20 mins between set waves). This swell should hold into Tuesday morning before easing through the day. 

Wednesday’s new swell (see source below) should rebuild to 8ft+ across most of the Margs region, but the extra S’ly component in the swell direction will create a wider range in wave heights from break to break. Size should persist into Thursday morning then ease. 

Note: these kinds of (very) long period events usually display a slightly different response between surf spots, all dictated by the local bathymetry. And, offshore bombies can significantly enhance wave heights, so there’ll be a couple of locations pulling in much larger surf than the regional average.

It's also worth noting that despite the size and strength of the swell energy, it's often the consistency (or lack thereof) that ultimately has the biggest influence on the quality of your session - even if the waves are great when they arrive, it's obviously harder to jag a set when they're extremely infrequent.

As for local winds, the main influence all of next week will be a heat trough along the coast that may receive a small reinforcement from a weak front (around Wed). This will maintain southerly winds across the region all week, with Monday and (especially) Wednesday at risk of the most strength. As such Tuesday and Thursday will see the cleanest conditions of the week - before lunch, ahead of the afternoon sea breeze - but Mon/Wed mornings may offer brief windows of light winds at dawn. 

As for Perth and Mandurah coasts, the Mon/Tues swell should build to 2ft+ in Perth and 2-3ft+ across the Mandurah stretch, and the Wed/Thurs swell may nudge a little higher. However the same wind risks are at play for Mon and Wed. 

Have a great weekend, see you Monday!


thermalben's picture
thermalben's picture
thermalben commented Monday, 19 Oct 2020 at 10:33am

Cape Naturaliste buoy picked up 20 second peak periods in the early hours of this morning (and has held there for the last four hours, which is a good sign).

New groundswell lines are now starting to show across the Margs region, though it's very inconsistent (and a little wind affected).


thermalben's picture
thermalben's picture
thermalben commented Monday, 19 Oct 2020 at 3:17pm

Slowly getting there.

Cetus's picture
Cetus's picture
Cetus commented Monday, 19 Oct 2020 at 7:00pm

Any more updates Ben?