South Australian Forecast by Craig Brokensha (issued Wednesday May 21st)

Best Days: This afternoon Mid Coast, tomorrow and Friday both coasts, Saturday South Coast

Features of the Forecast (tl;dr)

• Moderate to large sized W'ly swell building later today, peaking overnight, easing tomorrow
• Local offshore winds tomorrow AM, with weak PM sea breezes
• Large, powerful SW groundswell Fri AM (possibly showing later tomorrow), easing into the PM and Sat
• N/NW tending W/NW winds Fri down South, NE tending NW on the Mid without much strength
• Strengthening N/NW tending NW winds Sat (N/NE early Mid)
• Mod-large W/SW swell Sun with strong N/NW winds (building windswell in the Mid Coast)
• Large, stormy mix of swells Mon/Tue with gale-force NW tending W/SW winds Mon, strong but easing S/SW Tue

Recap

The Mid Coast was tiny and wind affected yesterday, great down South with offshore winds and an easing 2ft+ of swell across Middleton.

Today is nice and clean again on the South Coast with 1-2ft sets, tiny and to 1ft inside the gulf. Some new W/SW swell is due into this afternoon, with the Mid Coast expected to reach 2ft to possibly 3ft weak sea breezes.

This week and weekend (May 22 - 25)

This afternoon’s increase in W/SW groundswell was generated by a strong mid-latitude low pushing up and under Western Australia, with it due to produce 2ft to possibly 3ft sets across the Mid Coast later today, easing back from 2ft+ tomorrow morning with Middleton only due to see inconsistent 3ft sets thanks to the blocking effects of Kangaroo Island.

Local winds tomorrow look great with light, local offshore breezes ahead of relatively weak sea breezes.

Now later in the day we might see the fore-runners of our large SW groundswell showing across the regions, though Friday is still expected to reveal the peak in energy.

The ‘bombing’ low linked to the swell is currently weakening to the south of Western Australia while still generating fetches of W/NW gales.

Before the low weakened we saw a tight, very intense fetch of storm to hurricane-force winds, abating slowly through yesterday as the low expanded in scope and pushed east.

This has generated a large, long-period SW groundswell with it expected to peak Friday morning to 6ft+ across Middleton with 8ft sets on the deepwater reefs, and 2ft on the favourable parts of the tide across the Mid Coast.

Local winds look great for the South Coast and N/NW tending W/NW with early NE winds across the Mid Coast before shifting variable NW into the afternoon.

The swell is due to ease into Saturday back from 3-4ft across Middleton with strengthening N/NW tending NW winds (N/NE early on the Mid but tiny).

This strengthening wind will be ahead of a significant cold outbreak across the state, with a deep polar front due to project from the polar shelf towards the Bight through Friday/Saturday, moving across us slowly through Sunday/Monday.

Ahead of the storm proper, Sunday looks to see a moderate + sized W/SW swell from an initial front passing under WA towards the Bight Thursday/Friday, with the Mid Coast due to come around 2-3ft but with strong N/NW winds, whipping up some localised windswell.

The South Coast looks to see 3ft+ waves across Middleton, tricky with the strong offshore winds but clean and lined up.

Come Monday, the low will move across us proper, bringing gale-force NW tending W/SW winds and a large increase in stormy windswell across both the Mid and South Coasts.

The size is still up for grabs with GFS stalling the progression longer than ECMWF though we’re probably looking at 4-5ft waves inside the gulf and 10ft stormy surf developing down South later and more so into Tuesday.

Strong S/SW winds look to create poor conditions Tuesday, likely tending more S’ly Wednesday but well review this Friday.