Western Australia Surf Forecast by Craig Brokensha (issued Monday August 16th)

Best Days: Today, selected locations tomorrow morning across Margs and Mandurah, Wednesday morning Margs and Mandurah, Perth and Mandurah Sunday morning, Monday, Tuesday and Wednesday next week

Features of the Forecast (tl;dr)

• New SW swell building tomorrow PM, easing Wed with moderate N/NE-NE tending onshore winds tomorrow, variable tending onshore Wed
• Building W/SW swell Thu PM with strong NW tending W/SW winds
• Swell persisting Fri and Sat with fresh to strong W/SW winds
• Oversized SW groundswell building Sun, peaking into the PM with strong S/SW winds (S/SE early in Perth and Mandurah)
• Large, easing SW swell Mon and Tue with morning offshore winds

Recap

The swell dropped from Friday into the start of the weekend with a light, variable offshore across the South West though with lumpy conditions, cleaner and better to the north but smaller.

Our good new W/SW-SW groundswell due yesterday filled in bang on cue with clean 6ft+ surf across the South West, 2-3ft in Mandurah and 2ft sets across Perth with winds being favourable all day.

Today our secondary, less consistent W/SW swell has filled in keeping 6ft+ sets hitting the South West, 2-3ft in Mandurah and 2ft across Perth. Winds should remain favourable into this evening again so make the most of it before onshore winds kick again from Thursday.

This week and weekend (Aug 17 - 22)

After a great couple of days surf, we've got a couple more windows of favourable conditions before winds go onshore Thursday.

Today's swell will ease this afternoon and further into tomorrow morning while a new, mid-period SW swell fills in through the afternoon.

The source of this swell was an off axis fetch of gale-force NW winds moving through our swell window yesterday and we should see some good size spreading radially off the fetch mainly for the South West.

The South West should build to 5-6ft into the afternoon (a bit smaller early) with 1-2ft waves across Mandurah, 1-1.5ft in Perth. Morning winds will favour selected spots with a moderate N/NE-NE morning breeze, shifting W/SW across the South West and N/NW-NW in Perth and Mandurah.

Wednesday looks a touch better as the swell eases with variable S/SE winds across Perth and Mandurah, variable in the South West. Sets should ease from 4-6ft in the South West, 1-2ft across Mandurah and 1-1.5ft in Perth.

Moving into Thursday and we'll see a mid-latitude front approaching from the south-west, bringing strengthening, pre-frontal NW winds ahead of a W/SW change while a new W/SW groundswell is due into the afternoon.

This swell will be generated by a short-lived low firing up ahead of the mid-latitude front, producing a burst of W/SW gales through our swell window while slipping south-east.

The swell should kick to the 6ft range in the South West, 2ft across Perth and Mandurah but with that onshore wind.

The swell looks to ease from a similar size on Friday along with fresh to strong W/SW winds, similar Saturday but with an increase in mid-period W/SW swell from the mid-latitude frontal progression itself. Size wise it's nothing overly big with 6ft surf due to continue across the South West, 2ft in Mandurah and Perth but with low quality options.

Of greater importance is a strong polar low firing up on the back of the mid-latitude fronts, east of the Heard Island region on Thursday. A great fetch of severe-gale to storm-force W/SW winds will be projected through our south-western swell window, pushing further east towards the Bight on Saturday evening.

An oversized SW groundswell is due from this source, building Sunday and peaking late in the day. The South West should build to the 15th range, with 4ft sets in Mandurah, 3ft across Perth.

Winds will swing S/SW on Sunday across the South West, favouring protected spots with a period of S/SE winds likely around Perth and Mandurah.

Monday looks the pick with with E/SE offshore winds as the swell eases back from 10-12ft in the South West, 3-4ft in Mandurah and 2-3ft across Perth. Expect smaller surf Tuesday as the swell continues to drop with offshore winds.

Longer term a new, mid-period swell may be seen mid-week but we'll have a closer look at this on Wednesday.