WA's calm midweek window before Friday's front

Light winds, 3-4m swell, then the next front

Western Australia has traded a run of wet, windy fronts for a few days of calm, and the timing is a gift for anyone heading to the coast.

A cold front cleared the southwest on Sunday, and a ridge of high pressure has since built over the state to settle the weather through to Friday.

Expect mostly sunny days, light east to northeasterly winds of 15 to 25 km/h easing further by early afternoon, and a slowly fading swell.

The Bureau of Meteorology has the next cold front reaching the southwest on Friday, so this quiet spell has a firm use-by date.

Why the calm and the swell arrive together

The ridge sitting over southern WA is what flattens the local wind and clears the sky, giving the classic sunny winter lull between fronts.

Yet the ocean has a longer memory than the sky, and a southwest swell of 3 to 4 metres is still marching in from fronts that have already passed.

That swell eases to around 2.5 to 3 metres by the middle of each day as the last of the storm energy runs out.

So the coast stays powerful even under blue sky, because groundswell is born from distant weather, not the breeze you feel on the beach.

"The best surf of the week lands on the calm days, not the stormy ones, because the swell was made days ago and hundreds of miles away."

How the week plays out

The ridge holds firm through midweek before the next front lines up in the Southern Ocean and pushes toward the coast on Friday.

Ahead of it, winds will swing to the north and freshen, the first sign the settled window is closing.

Behind Friday's front, expect a return to showers, stronger winds and a rebuilding swell into the weekend.

This front-ridge-front rhythm is the engine of a WA winter, and reading it a few days out is how you plan a good session.

What it means on the water

For surfers, this is a quality window: a solid 3 to 4 metre southwest groundswell under light morning easterlies that groom the face clean.

Get out early, because those offshore mornings give way to lighter, more variable winds by afternoon as the ridge weakens the gradient.

Exposed reefs and points will be pumping, but the size means heavy water, strong rips and closed-out sandbars for the less experienced.

For boaters, the light winds are inviting, but a 3 to 4 metre swell still stacks up dangerously at exposed bars and rock ledges.

Check the bar before you commit, cross on the top of the tide, and remember that a sunny sky does nothing to shrink a big groundswell.

Beach and rock fishers do well in this pattern, with the churned water and steady swell keeping tailor, herring and Australian salmon on the chew.

Work the deeper gutters and the edges of the whitewater where the swell stirs up food, and fish the change of light for the best results.

Respect the leftover swell

The biggest trap this week is complacency, when calm air and sun make a 3 to 4 metre swell look smaller than it really is.

Rock fishers should never turn their back on the sea, should wear a lifejacket and cleated boots, and should pick a ledge with high, dry escape ground.

Winter water off WA is cold enough to sap strength fast, so dress for immersion and keep a close eye on anyone in the water.

Common questions

How long will the calm last?

Through to Friday, when the next cold front is forecast to reach the southwest and bring back active weather.

Why is the swell so big on a sunny day?

Groundswell travels for days from distant fronts, so the ocean stays powerful long after the local wind drops away.

Is it safe to cross the bar?

Only with care, because a 3 to 4 metre swell can close bars without warning, so check conditions and cross at high tide.

When is the best surf?

Early morning, while the light easterlies hold offshore and before the winds turn variable in the afternoon.

Plan your window with the Seabreeze Perth wind forecast , and check the latest WA coastal warnings before Friday's front arrives.