Fresh S/SW swell for West Oz on Saturday

Ben Matson picture
Ben Matson (thermalben)

Western Australian Surf Forecast by Ben Matson (issued Thursday 29th March)

Best Days: Fri: smaller surf in Margs with reasonable winds. Expect a late kick in size from a new swell. Very small in Perth. Sat: solid S/SW swell across Margs with good winds. Only small in Perth. Sun AM: easing but good surf early with light winds. Remaining very small in Perth.

Recap: Wednesday saw a building swell that reached a solid 10ft+ across many exposed stretches, though offshore bombies and more favourably aligned swell magnets were considerably larger. North Point came in around size expectations with inconsistent 4-5ft sets (a couple of bigger waves from time to time) and conditions were clean with offshore winds. Surf size was much smaller in Mandurah and Perth with set waves between 1-2ft and 3ft+ depending on exposure. Today we’ve seen surf size ease; down to 1-2ft in Perth, a little bigger in Mandurah but still solid across the Margs region with 8ft sets early morning now easing to around 6ft this afternoon. Winds are offshore (fresh in the south) so it’s clean if a little blustery around Margaret River. 

This week and weekend (Mar 31st - Apr 2nd)

Note: Forecaster Notes will be somewhat brief this week as Craig’s on leave.

No changes to Tuesday’s Forecaster notes.

Today's easing trend will continue to ease into Friday, and winds will swing to a moderate SE breeze as a high pressure system ridges in from the south-west. Locations with good southerly exposure throughout Margaret River should see occasional 3-4ft sets in the early morning (with a possible easing trend through mid-morning), whilst Perth will see tiny conditions and Mandurah may have a few 1-2ft leftovers at exposed beaches. Conditions will be clean though just about everywhere.

Lunchtime should herald the arrival of the leading edge of a new S/SW swell generated by a broad, intense polar low that developed on the eastern periphery of the state’s S/SW swell window mid-week. As per yesterday’s swell that was of a similar direction - though with more size - we’re looking at a wide range in size across the region depending on exposure to the south. 

This swell is expected to peak on Saturday however Friday’s late session could see similarly sized sets as the peak is expected to plateau for quite a decent length of time (owing to the storm’s considerable development cycle). So, we may see 6ft+ sets across the Margs region on dusk with possible bigger bombs - but confidence is not high on how much size will push through (Wednesday's swell seemed to fall behind model expectations, probably the result of the S/SW swell direction, so this characteristic is possible for this swell too).

However this swell won’t properly reach the Perth and Mandurah coasts until very late (more likely overnight), of which the direction is expected to be generally unfavourable for these regions. Mandurah may see a late upwards trend into the 2ft+ range if we're lucky.

Saturday should see steady 6ft+ sets across south-exposed locations in Margaret River, possibly bigger at times near 8ft, with a slight easing expected in the afternoon. Conditions are looking great with early light offshore winds and afternoon sea breezes. 

Up closer to Perth we’ll see only small surf on Saturday, reaching a very inconsistent 1-2ft at Perth’s exposed beaches, with occasional 2ft+ sets at similarly exposed beaches in Mandurah. 

Surf size will then trend down on Sunday. Margaret River should see 4-5ft sets early, down to 3-4ft into the afternoon, and early NE winds will swing N’ly then possibly NW as a weak trough develops along the coast. Expect very small surf in Perth and not a lot of size in Mandurah either. 

Next week (Apr 3rd onwards)

Still nothing significant expected at all next week. The storm track will become rather quiet from now through the weekend leading to small surf in all areas through the first half of next week, including Margaret River (for size reference, expect slow sets either side of about 3ft in Margs from Mon to Wed, with a temporary low point some time on Tues). 

A reasonable front and low developing near Heard Island on Sunday should kick up a modest new swell for next Thursday, but no major size is expected, and it'll be very inconsistent - probably some 4-5ft+ sets across the Margaret River coast but remaining small throughout Perth and Mandurah. A new ridge of high pressure will drive fresh S/SE winds across the region at this time which is workable not but perfect.

A significant polar low is expected to develop behind this, much further wet, but its alignment doesn’t look great for the WA coast and there associated swell isn’t due until the middle of next weekend - it’ll be an extremely inconsistent, long period event with early indications for wave heights around the 4-6ft range in Margaret River. 

I'll have more in the next update on Saturday.


thermalben's picture
thermalben's picture
thermalben Friday, 31 Mar 2017 at 5:31pm

No sign of the leading edge of the expected new S/SW swell at Albany yet so an increase later today (across the Margs coast) is very unlikely. 

Sheepdog's picture
Sheepdog's picture
Sheepdog Saturday, 1 Apr 2017 at 1:02pm

Waaaaaaaaay undercalled

thermalben's picture
thermalben's picture
thermalben Saturday, 1 Apr 2017 at 1:35pm

Yeah surf size is peaking higher than expected. Though interestingly, buoy data is smaller than Wednesday's swell - Albany (directly open to the S/SW swell direction) is almost 2m smaller, and Cape Naturaliste is around 1m smaller.

The size difference in surf height therefore has to be a combination of (higher) swell periods and local bathymetry.

Sheepdog's picture
Sheepdog's picture
Sheepdog Saturday, 1 Apr 2017 at 1:42pm

maybe a touch more sw?

thermalben's picture
thermalben's picture
thermalben Saturday, 1 Apr 2017 at 1:59pm

Swell direction is a touch more SW than S/SW (compared ot the last one).. that could indeed be a factor.

But this still neglects the fact that wave height data are smaller at both buoys compared to Wed's swell. Irrespective of the swell direction, there should be a correlation between buoy data (esp Cape Nat) and surf size.

This leads me to believe that it's swell period and (more crucially, but far less understood) local bathymetry.