Sizeable swells incoming, though windy at times

Western Australia Surf Forecast by Ben Matson (issued Monday 19th October)

Best Days: Tues/Wed/Thurs: pulsey long period swells though very windy at times. Early mornings should see periods of more moderate S/SE breezes. Quite large in Margs Wednesday. Thurs onwards: more manageable conditions with easing swells and lighter winds. Next week: more large swells on the way. 

Recap: Small residual swells and early offshore winds padded out the Margs region over the weekend, with no appreciable surf across metro coasts. The leading edge of the expected first long period groundswell reached WA coasts in the early hours of this morning, with peak swell periods around 20 seconds. Although surf size was very small early on (2-3ft in Margs, tiny across metro coasts), we’ve seen a strong though inconsistent building trend throughout the day with afternoon sets around 6-8ft. However, gusty southerly winds have caused problems at all but the most protected locations. Surf size seems to have reached 3-4ft in Mandurah late in the day (with fresh S/SW winds) but Perth was looking a little slow on dark with 1-2ft sets, and lighter SW winds. 

Chunky, tho' windy in Margs Monday afternoon

Lunchtime lines at Yallingup

Strong Monday arvo sets in Mandurah

Not much happening in Perth early evening

This week (Oct 20 - 23)

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

So, the first swell has come in very close to expectations, slightly above in Margs and Mandurah, but slightly under in Perth, however with the building trend being accompanied by gusty winds there wasn’t many surfable options. 

This swell will ease slowly into Tuesday and we should see a relaxing of S/SE winds early morning. Expect early though very inconsistent 6ft+ sets across the Margs region, 2ft in Perth and 3ft in Mandurah, easing during the day and becoming very choppy again after lunch as the coastal trough intensifies. 

Similar winds are expected Wednesday, in fact we’ll probably see even stronger afternoon breezes throughout the Margs region as a weak front merges with the trough, and enhances the synoptic S/SE flow. 

Late Tuesday afternoon, we may see the leading edge of the next round of groundswell nose into the coast, generated by an incredible Southern Ocean Low currently to our south-west.

On Sunday it displayed a broad fetch of 50kts winds; this was on top of three or four days prior of strong activity through the state’s far swell window. It’s still generating energy right now (see chart below), though most of the work has been done on the eastern periphery of our swell window, which means the resulting swell direction will be a little more SW thru’ S/SW. 

Anyway, this swell will kick in overnight and provide a powerful surf through Wednesday. Based on the ASCAT readings from yesterday, and today’s wave heights punching on the upper end of size estimates, I’m going to nudge Wednesday’s forecast up a little more to 8-10ft+ throughout the broader Margs region. 

There’s a couple of other points worth reiterating from Saturday’s notes. That is, Wednesday’s surf won’t be anywhere near as inconsistent as today (and tomorrow), because we’ll see two swells in the water - the sizeable new energy sitting on top of decaying energy from the previous days. This will help to reduce the perceived inconsistency.

Also, expect a slightly different response (in size) between surf spots, as this is dictated by the long swell periods reacting to the local bathymetry. Most notably, offshore bombies will significantly enhance wave heights, so don’t be surprised if reports come in from the usual suspects where it’s much larger than the regional average.

Anyway, even though we’ll see strong, sizeable surf all day, you’ll have a limited window of clean options early morning before the wind strengthens from the S/SE. 

Across Perth and Mandurah coasts, the extra southerly component in the swell direction won’t favour these locations for a great deal of size but we should still pick up 2-3ft and 3-4ft+ surf respectively (before the afternoon S/SW breeze kicks in). 

Easing swells are then expected through Thursday and Friday with a more moderate wind regime from the SE tending SW. Thursday morning should still be pretty solid early on (6ft, maybe 6-8ft exposed Margs spots) but you’ll have to aim for the early session for the most size and best conditions. It’ll be small across metro beaches to finish the working week.

This weekend (Oct 24 - 25)

With no new swell expected Saturday and only a faint, long range groundswell due Sunday, we’ll be back to the exposed beaches and small wave reefs in Margs this weekend.

Size should ease from 3-4ft to 3ft here, and it’ll be very small in Perth and probably just borderline rideable across the Mandurah stretch.

Fortunately, a weak synoptic pattern will result in light morning winds and moderate afternoon sea breezes. 

Next week (Oct 26 onwards)

An amplifying Long Wave Trough is expected west of WA over the weekend, which will generate a couple of rounds of sizeable waves with periods of onshore winds kicking in at times.

The first new swell is due Tuesday and Wednesday, with the second arriving on Thursday and Friday - though the second event will be much bigger in size, and we may be lucky to see local winds ease right back in strength as the associated front slips to the SE. 

So, there’s plenty more action lining up for the long term.

See you Wednesday!


Redmond Clement's picture
Redmond Clement's picture
Redmond Clement commented Tuesday, 20 Oct 2020 at 12:45pm

Comprehensive again Ben, thanks, should add some erratic arrows.

thermalben's picture
thermalben's picture
thermalben commented Wednesday, 21 Oct 2020 at 10:31am

Not small!

thermalben's picture
thermalben's picture
thermalben commented Wednesday, 21 Oct 2020 at 10:36am

Kellya's picture
Kellya's picture
Kellya commented Wednesday, 21 Oct 2020 at 1:35pm

Mandurah Wedge cam seeing a bit of action