Average weekend of waves; excellent large groundswell peaking Tuesday

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Ben Matson (thermalben)

Western Australia Surf Forecast by Ben Matson (issued Friday 14th October)

Best Days: Perth/Mandurah: Sun AM, clean peaky beachbreaks. Tues: clean groundswell, best suited to the reefs. Margaret River: Sat, Sun AM: solid surf, best suited to protected bays and points. Late Mon/Tues: large groundswell, with excellent conditions early Tues.

Recap: Onshore winds have maintained poor conditions across both coasts over the last few days, with swells building slowly through Thursday ahead of a more rapid increase in size this afternoon. 

This weekend (Oct 15 - 16)

The synoptic chart says it all: a cut-off mid latitude low just SW of the state is driving strong westerly winds into the lower SW of Western Australia. At its core, a small tight fetch of 30-40kt winds is wrapping clockwise around the low, generating large SW swells for the region.

However, short range swells necessarily aren’t a great candidate for good surf across this coastline. First of all, local winds remain poor and secondly, the region’s abundance of reef breaks are better tuned to long period groundswells from distant sources. The random, peaky nature of these short range events results in chaotic lineups at times and the swell lines are often not defined enough to consistently wrap into protected locations.

That being said, Saturday will certainly offer an improvement with the current W’ly wind regime expected to swing SW and then S/SW throughout the day. Along with building swells (that could reach 10-12ft at exposed spots down south) we should see smaller, cleaner conditions inside the protected bays and points across the Margaret River coastline. 

The Perth and Mandurah coasts won’t fare quite as well, as there are limited protected options under these winds. Some of the groynes may offer partially better conditions but the swell will have a lot of south so many of these locations will be smaller. Expect 3-4ft surf across the exposed Perth metro beaches and up to 3-5ft in Mandurah.

Sunday will present much cleaner conditions as a high quickly ridges in from the west, creating much lighter S’ly winds about most coasts. We should see a slightly SE trend early morning across the Perth/Mandurah stretch, but it’ll remain S/SW across the Margaret River coastline.

However, surf size will be easing throughout the day, from 8-10ft to 5-6ft down south, and 3ft down to 2ft across the Perth metro beaches (a little bigger in Mandurah).  Protected bays and coves around Margaret River should have some decent small clean waves in the morning before it loses too much size.

So, Sunday morning looks like the pick of the weekend - but don’t expect anything amazing at either coastline. 

Next week (Oct 17th onwards)

Easing swells are expected Monday, with moderate S/SW winds across the Margaret River coastline as a front clips the region. We should see early light S/SE winds throughout Perth and Mandurah ahead of the afternoon sea breeze, but surf size will be small, around 1-2ft in Perth with occasional 2-3ft sets across the open Mandurah beaches. Margaret River should still be somewhere in the 3-5ft range. 

This front (clipping the coast) will be the northern extremity of a deep Southern Indian Ocean low that’s developing SE of Madagascar today, and is expected to strengthen through our SW swell window over the weekend as it tracks eastwards. Although positioned a little too far south for my liking (relative to WA coasts), and reaching maturity a little too far to the east, it’ll still display a long, intense fetch - aimed just south of our region but still in a great position for swell production.

This is expected to generate a strong SW groundswell that should arrive across the Margaret River coastline late afternoon on Monday, peaking in size on Tuesday. And the great news is that a weak right of high pressure will generate light offshore winds ahead of a shallow afternoon sea breeze for Tuesday. 

At this stage we should be looking at a peak somewhere the 10-12ft+ range across the Margaret River coast on Tuesday, with significantly bigger waves at offshore bombies owing to the long swell period (likely in the 16-17 second range early Tuesday, down from late Monday's leading edge at 17-18+ seconds).

It’s hard to tell how much of a size kick we’ll see late Monday as a few hours could make a substantial distance. A reasonable estimate would be for set waves to be pushing 6-8ft+ right on dark, maybe bigger - but probably only in Margaret River (it probably won't reach Mandurah or Perth until after dinnertime). 

This swell should also produce good 2-3ft waves across the Perth metro beaches on Tuesday, and 3-4ft+ surf across open Mandurah beaches. 

Looking further ahead and easing swells are then expected from Wednesday onwards with no sign of any significant events beyond this.

Have a great weekend, see you Monday!