Large surf Wednesday, easing Thursday ahead of a solid S/SW swell late Friday onwards

Ben Matson picture
Ben Matson (thermalben)

Western Australian Surf Forecast by Ben Matson (issued Tuesday 28th March)

Best Days: Wed: Large swell across the Margs region with good winds. Should be big enough for protected locations (though considerably smaller due to S/SW swell direction). Small clean waves across Perth and Mandurah. Thurs: Large but steadily easing swell with good winds in general. Only small in Perth and Mandurah. Sat/Sun: solid S/SW swell with generally good winds in the Margs region. 

Recap: Solid swells across the state on Saturday built further on Sunday with a new long period swell, with Monday seeing another small increase in size with exposed locations topping out around the 10-12ft mark in Margaret River. Perth and Mandurah have seen fun waves with light winds and 2-3ft surf across metro beaches today, a little bigger in Mandurah. Wave heights have since eased into this morning, with Margs around 6ft+ and the Perth metro beaches around 2ft. Winds are light offshore north of Bunbury but still moderate onshore across the Margs stretch.

This week (Mar 28th - 31st)

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

We’re at the bottom of the current swell cycle, with a new long period S/SW groundswell expected to build in the early hours of Wednesday morning

This swell was generated by the tail end of a broad, intense frontal progression through the Southern Ocean. The vast majority of this system lies east of Margaret River longitudes and is thus aimed best towards South Australia and Victoria. As such we will see a (relatively) smaller spread of swell across WA coasts. 

The eastern position of the storm track will also result in a more southerly swell direction than what we typically see across this region. This will display a range of outcomes across various coasts: throughout the Margaret River region, there'll be a much larger difference between exposed locations and protected bays and points (this will also affect surf size at North Point, which has been confirmed as the opening location for the WSL event on Wednesday). Local bathymetry will steer the long period energy into specific locations so don’t be surprised if some locations are bigger than expected, whilst other locations are smaller than expected. Each swell has its own unique charcteristics (period, direction, height) and they all have a bearing on eventual surf size at individual suf breaks.  

North from Cape Naturaliste, we’ll see much greater shadowing effects across the Mandurah stretch (thanks to the curve of Geographe Bay) and Perth metro beaches (owing to Rottnest Island). This will create relatively small surf for these regions. 

Fortunately, high pressure will move in from the west tonight, swinging today’s onshores (across the Lower SW) around to the SE. Exposed locations may see some early wobble but for the most part it’ll clean up a lot.

As for size? Our surf model typically undercalls long period energy across the Margaret River region, so I’m expecting set waves in and around the 8-10ft+ mark at most open reefs (i.e. Main Break) on Wednesday. Some deepwater offshore reefs should be quite a lot bigger. But, protected bays and points will see considerably smaller surf. 

And with the WSL in town I can’t shy away from a call on North Point.

Whilst I am quite concerned with how much size will be lost due to the strong southerly component in the swell direction, I think it’s a good decision to prepare for North Point on Wednesday - because Main Break in the 10ft range is quite unruly, and not neccesarily an ideal competition wave.

Using yesterday’s images as a reference (see here), and with wave heights expected to be smaller at exposed spots - plus with the extra south in the swell direction - I think we’re probably looking at 4-5ft sets at North Point. The swell direction will also have an effect on consistency, lowering it a little. Conditions should be very good here though with moderate E/SE thru’ SE winds (there may be some chatter up the face if the wind gets above 12-15kts, but we should be good for the most part).

As for locations further north - Perth should see an increase during Wednesday into the 2ft+ range by the afternoon (smaller earlier), with Mandurah likely to be a little bigger around the 2-3ft mark. Both coasts will be clean with light offshore winds. 

Moving right along, and Thursday is looking great for the morning session down south. 

An intense Southern Ocean low will be passing well to the south at this time, so the WA coast will be 'between ridges' - resulting in early light E/NE winds ahead of a moderate southerly sea breeze in the afternoon. Surf size will be easing steadily from Wednesday; Main Break should see set waves in the 6-8ft range early Thursday morning but will be down to 4-6ft by the afternoon, maybe smaller by the end of the day. Again expect a wide range in size between south-exposed locations and protected spots. 

Up in the Perth and Mandurah regions we’re looking at much smaller fading swells (1-2ft and 2ft+ respectively, smaller later).  

Friday morning will then see a further drop, with moderate to fresh SE winds becoming established across the region as the new high muscles in from the west. Margs should maintain sets around the 4ft mark though it’ll be very small in Perth and Mandurah.

The intense low passing south of the state on Thursday looks quite incredible on the MSLP charts - if you’re in SA or Vic, that is. Once again, this system is going to reach maturity as it exits Western Australia’s acute southerly swell window, and this means we’re looking at a much smaller spread of long period S’ly swell across the Margs coast, and very little swell pushing north into Mandurah and Perth.

The leading edge of this swell should arrive on Friday afternoon ahead of a peak in size (from a secondary, stronger pulse) on Saturday). Late Friday could see some 5-6ft sets at Mainbreak but by this time we’ll be under a fresh S/SE breeze. 

This weekend (Apr 1 - 2)

The long period S/SW swell pushing through Margs on Friday is expected to reach a peak on Saturday and the good news is that the high pressure system west of the state will weaken slightly, reducing the pressure gradient and thus lowering the wind speeds. 

I can’t overstate just how much these acute S/SW swells create a wide range in surf size across the coast. Some exposed locations could see easy 6-8ft sets (if you’re on the southern WA coast, or at a well focused offshore bombie, you can almost double that figure) however protected locations in and around the Margs region will be much smaller. 

As such I’m not expecting Saturday’s swell to be big enough for North Point - though I’ll revise this more closely upon what happens tomorrow. Main Break should however be somewhere close to the upper end of this size range (i.e. 6ft+). 

This swell will then ease through Sunday with early NE winds possibly swinging N’ly though without any major strength. Main break should manage 4-6ft sets early, easing to 3-4ft throughout the day. Expect much smaller surf elsewhere. 

Up across the Perth and Mandurah coasts I’m not expecting this new S/SW swell to make much of an impact. Saturday could see some 2ft+ waves around open Mandurah beaches with occasional 1-2ft waves in Perth but that’s about it. Conditions will however be clean here. 

Next week (Apr 3 onwards)

There’s nothing amazing standing out in the long term outlook for next week.

I’m seeing a steady progression of fronts through the Southern Ocean though nothing that’s likely to kick up exposed locations around the Margs region significantly higher than the climatological norm (of around 4ft). Winds do look favourable through the early to middle part of the week with a frontal progression possibly bringing in a northerly spell around Friday ahead of a western flow next weekend. 

More on this in Thursday’s update. 


Halfscousehalfcockneyfullaussie's picture
Halfscousehalfcockneyfullaussie's picture
Halfscousehalfc... Tuesday, 28 Mar 2017 at 7:38pm

I don't have a lot of knowledge about wa or the surf spots, but from what I read, doesn't north point only start breaking properly at 6ft? If so 4-5 foot sets surely is not going to be good enough for the comp at np tomoz