Western Australian Forecast by Lorena Woortmann (issued Wednesday May 18th)

Best days: Thursday morning at Perth and Mandurah, Monday morning at Perth and Mandurah, Tuesday at Perth and Mandurah, Wednesday at Perth and Mandurah and Wednesday morning at Margs

Features of the forecast (tl;dr)

• WSW groundswell building this PM to 8ft at Margs, 2-3ft at Perth/Mandurah
• Blown out this PM with strengthening W winds
• WSW groundswell Thurs AM to 8ft+ at Margs, 3ft+ Perth and 4ft+ Mandurah
• Lumpy at Margs with an OK early window
• Light and variable winds at Perth and Mandurah 
• Long period WSW swell Friday AM building to 8-10ft+ at Margs but onshore
• Early ENE window at Perth and Mandurah with 3ft surf at Mandurah and 2ft a Perth
• Reinforcing pulse Saturday PM into Sunday 10–12ft Margs and 3–4ft metro regions
• Onshore weekend across the coast 
• Easing swell into Monday
• Series of SW pulses from Monday PM to Wednesday
• Improving winds at metro regions Monday late AM/PM with leftover surf
• Fun conditions up north on Tue with 2-3ft Perth and 3ft+ Mandurah
• Fresh SW winds at Margs
• Wed AM offshore at Margs and Mandurah, clean all day at Perth 
• Easing trend into late next week

Recap

Yesterday we saw the groundswell easing, Perth had clean 2-3ft waves on offer and winds held light through the day as the surf dropped in size, while Mandura saw slightly stronger winds with a more northerly direction. At margs winds were fresh out of the North and it wasn’t perfect, but there was something for the keen. 

This morning we saw already the closer range swell filling in with a NW direction for the metro regions and WSW for the South West, from the remnants of a low that pushed close to the coast. This system brought more northerly winds that weakened into the morning at Margs which saw clean faces and 5-6ft+ of WSW swell. Perth got some heavier weather from this system and NNE/ENE winds with fun, consistent and peaky surf at the 3ft range in the morning before freshening winds, while Mandurah had fresher winds and bumpier conditions. 

This week (Jun 18 - 20)

The longer period WSW pulse should keep filling into this afternoon and the size at Margs should go up to 8ft, metro regions will drop to 2ft as the groundswell has a WSW direction and the NW wind swell eases. But by the afternoon the surf will be blown out as the winds turn westerly across the coast.

For tomorrow morning we are expecting another long period WSW swell from the earlier stages of a low that broke down into the weather we saw on the cost today. There’s a chance of variable winds at Margs in the early morning with 8ft+ surf, but even with this window the surf will still be lumpy from today’s onshore winds and westerly winds out to sea. Perth and Mandurah will see fun conditions with light and variable breezes in the morning and 3ft+ at Perth and 4ft+ at Mandurah.

As touched on the last notes, we have a large and strong WSW groundswell expected for Friday morning, generated by a broad frontal progression through the Southern Ocean pushing eastwards towards WA.  

However for Margs, the winds will remain onshore until next week as we have a trough that crosses the coast tomorrow night and develops into a low pressure system off the southern coast of WA into Sunday. This low development stalls the trough over WA and delays the movement of the high pressure system that would otherwise improve conditions, with another front coming right behind it.

Metro regions will see the trough approaching a little later and might still have an early window of ENE winds Friday morning before it deteriorates through the day and remains onshore until early next week, with the surf staying in the 3ft range at Mandurah and 2-3ft at Perth before picking up on the weekend but with poor conditions.

This weekend (Jun 21 - 22)

With that system moving in, the weekend doesn't look like inviting with onshore winds. The reinforcing pulse expected for Saturday afternoon will be overwritten by local swell that builds into Sunday and the surf will be large and onshore, with 3-4ft at Metro regions and 10-12ft at Margs, easing into Monday. 

Next week (Jun 23 - 27)

Conditions should start improving around the metro regions from Monday late morning/afternoon, with a small leftover surf at the 2-3ft range.

From late Monday afternoon to Wednesday we have a mix of SW swells from a constant train of activity slowly moving east on the Southern Ocean starting from south of South Africa and progressing past Heard Island with lots of bursts and re-intensifications. These pulses will send sizes on Tuesday morning to the 8ft+ range for Margaret river, 2ft Perth with the occasional 3ft, and 3ft+ at Mandurah. 

Tuesday should be fun at the metro regions with offshore winds, and while winds do go lighter at the South West, they will still be out of the SW and onshore on the west coast, with the protected spots on the north end seeing better conditions but smaller with this swell direction.

As the high pressure quickly moves over the coast overnight on Tuesday, Margs and Mandurah will have a window on Wednesday morning with offshore winds before they tend NNE, while Perth should see clean conditions most of the day. 

Into late next week and the weekend we should see an easing trend with a WSW pulse expected for the weekend, which we will look at again on Friday.