Western Australian forecast by Steve Shearer (issued Mon March 10th)

Features of the Forecast (tl;dr)

• Fun waves hold into Tues for the SW
• E/SE winds Tue AM
• Mod-large, SW groundswell building later Wed, peaking Thu
• NE tending variable then NW-W winds Wed
• Period of NE winds still possible Thurs depending on trough of low pressure off SW corner
• Variable tending S/SW-S winds Fri
• Large SW groundswell likely later Fri, peaking Sat AM with E/SE winds

Recap

Not much on Sat with small onshore surf but by Sun surf picked up to 4-6ft between the Capes, small 1ft in Perth and Mandurah with SE tending S’ly winds. Surf has held into this morning with sets to 6-8ft in the SW corner, remaining small 1ft or so in Perth and Mandurah with cleaner conditions under E/SE-SE winds and late seabreezes. 

Some solid sets this morning with offshore winds

This week and next week (Mar 10 - 21)

The Indian Ocean is in an active phase with a storm track concentrated on disturbances SW of Heard Island and tracking below the state maintaining intensity. Locally, a ridge under the state is being enhanced by a trough moving down the coast from the Gascoyne, eventually forming a low off the SW corner before it moves inland again. 

We’ll moderate SW swells from the current storm set-up passing under the state with plenty of windows of workable or good winds. Larger swells are on en route for the weekend.

In the short run we’ll see more offshore E/SE-E winds in the morning, tending to light/late seabreezes. Today’s swell eases back to 3-5ft at exposed breaks in the SW, smaller 1ft in Perth/Mandurah. 

Similar into Wed AM but by mid-morning or just after we should see longer period SW swell fill in to 4-6ft across the SW, smaller 2ft in Perth and Mandurah. Conditions should remain clean under light offshore winds, tending variable then NW-W/NW as a trough of low pressure moves offshore. 

We should see size holding through Thurs before a slow easing into Fri morning. Winds look tricky with the trough of low pressure off the SW but we should see light N-NE winds for a time Thurs, with winds shifting NW.

On Fri a period of offshore/variable winds is likely before the trough moves eastwards and brings a S’ly flow. 

A storm force system tracking between 70-90E Tues/Wed (see below) generates seas in excess of 40ft SW of WA. Long period forerunners arrive Fri evening with inconsistent sets to 5-6ft. The bulk of the swell energy in the 15-17 second band fills in Sat with sets to 8-10ft across the SW reefs, smaller 2-3ft in Perth and Mandurah. Winds will be a bit unruly with a SE-S/SE flow early, tending mod S’ly then S/SE again late in the day. 

Size eases into Sun with winds shifting E-E/SE as high pressure slips beneath the state. 

A long zonal fetch well to the SW of the state supplies plenty of residual energy in the 3-5ft range through Mon-Wed next week with SE-E winds likely as high pressure remains below the state. 

Lots more activity ahead with a storm force low likely to form in a sharp trough near Heard Island this weekend.

We’ll see how that looks on Wed.