Western Australia Surf Forecast by Craig Brokensha (issued Wednesday 18th December)

Best Days: Saturday morning in the South West and Mandurah, Wednesday morning, Thursday morning

Recap

Building surf across the South West yesterday morning with favourable conditions early, deteriorating shortly thereafter. The swell became large into the afternoon but with strong onshore winds. Perth and Mandurah started tiny but kicked into the afternoon.

Today a reinforcing W/SW swell and better offshore winds is providing good waves across all locations with surf to 4-6ft in the South West, 2ft in Perth and Mandurah on the sets.

This week and weekend (Dec 19 - 22)

Developing onshore winds this afternoon will be linked to a strong mid-latitude low moving in from the west, with an upgrade in the strength of the system since Monday.

We'll see a tight fetch of strong to near gale-force W/SW winds projected towards and then into us tomorrow afternoon and evening, creating poor conditions and kicking up a weak windswell, followed by the mid-period W/SW energy on Friday.

Size wise, Margs should see messy and low quality surf to 6ft, easing through the day with 2-3ft sets in Perth and Mandurah.

Unfortunately winds will remain onshore from the SW tending S/SW across all locations Friday, offshore Saturday from the E/SE tending E/NE in the morning but on the way out. Easing sets from 4-5ft are due in the South West, 1-2ft in Mandurah and 1-1.5ft Perth, while a small reinforcing S/SW swell on the cards for the South West is now forming too late in our swell window. Only a few select south magnets on the southern end of the Cape are likely to see it, kicking to 4-5ft+ through the day.

Come Sunday a weakening front approaching from the west-southwest will bring onshore S/SW winds with a small leftover mix of swells.

The earlier stages of the weakening front will generate a new mid-period SW swell for Monday afternoon and more so Tuesday though not to any major size. Morning S/SE winds Monday morning will create less than ideal conditions ahead of the swell, with Tuesday being less favourable with S-S/SW winds. Margs should see sets to 3-4ft+, tiny further north.

Of greater importance are better W/SW swells due into the middle and end of the week, generated by a good frontal progression developing west-southwest of us on Sunday. An elongated fetch of strong to near gale-force W/SW winds will be projected towards us, weakening but followed by trailing weaker fronts through the week.

A good moderate to large sized W/SW swell is expected off this initial progression, building slowly Wednesday and reaching 6ft+ late afternoon across the South West, 2-3ft in Mandurah and Perth, easing from a slightly smaller size Thursday.

Winds look to improve and swing offshore from the E/SE on Wednesday morning and E/NE Thursday, creating great conditions. More on this Friday though.