NSW hazardous surf builds to 3 m south swell

Warning covers Thursday and Friday, Byron added

The warning starts tomorrow, not today. BOM issued Hazardous Surf Warning IDN28522 at 4:53 am EST on Wednesday 9 September, and it stays in force through to midnight EST on Friday 11 September.

Wednesday is about the wind and the front itself, while Thursday and Friday are about the swell the front leaves behind it.

A cold front is crossing eastern NSW today, bringing showers and fresh to strong southerly winds in its wake as it pushes up the coast.

Sydney Coastal Waters. The Sydney forecast IDN11009, issued at 10:00 am EST Wednesday, has west to south-westerly winds of 15 to 20 knots turning southerly at 25 to 30 knots around midday.

Seas start below 1 m and lift to 2.5 to 3 m through the afternoon, with south swell at 1 to 2 m building to 2.5 to 3 m later in the evening.

Thursday holds southerlies of 15 to 25 knots, up to 30 knots early, with seas of 2 to 2.5 m easing to 1 to 1.5 m through the morning while the south swell sits at 2.5 to 3 m.

That is the combination that catches people out, because the wind backs off, the whitecaps go flat and the swell keeps arriving on schedule.

Friday has southerlies of 10 to 15 knots becoming variable, with south swell of 2 to 3 m easing to about 2 m by evening.

BOM keeps a hazardous surf caution running right through Friday for that exact reason, along with a caution for large and powerful surf around bars and rock fishing spots.

Illawarra. The Illawarra forecast IDN11010 has southerlies of 20 to 30 knots today, seas of 2 to 3 m by midday and south swell reaching 2.5 to 3 m in the early evening.

Thursday keeps that south swell at 2 to 3 m, and Friday holds 2 to 2.5 m before it starts to trim down.

Wollongong, Port Kembla and Kiama sit square to a due south swell, so the reefs and points will be loaded up while the open beaches close out.

The doubling caveat. BOM's standard note on warnings like this one is that maximum waves may be around twice the forecast height.

Take that at face value and a 3 m south swell can throw sets in the order of 6 m across a low rock platform.

That figure is BOM's own caveat rather than a measured wave, and it is the number worth thinking about when you are standing on wet rock with your back to the water.

NSW Police Force Marine Area Command has issued the standing advice that goes with these warnings.

Stay out of the water and avoid walking near surf-exposed areas. Rock fishers should avoid exposed rock platforms. Boaters should consider delaying bar crossings, wear a lifejacket and log on with Marine Rescue.

Bars versus the open ocean. Inside Sydney Harbour the water will look workable, but the entrance and the ocean beyond it are a very different proposition on Thursday morning.

The Port Hacking and Broken Bay bars will both be working on a rising south swell, and the Ulladulla bar deserves a long look from the shore before anyone commits to it.

Boaters heading out of Newcastle and the Hunter should expect strong rips and a short, confused sea until the wind chop settles back on Thursday.

Beaches. Bondi, Maroubra and Cronulla are all likely to close out on the bigger sets, with strong rips digging along the banks between them.

Newcastle and Hunter beaches will run the same pattern, and Coffs sits inside the Thursday warning area as the swell energy tracks further north.

The Byron Coast is added on Friday, which marks the northern edge of this event before the swell fades out.

Many beaches are not fully patrolled this early in the season, so the safest call for anyone unsure is to stay on the sand.

Rock fishing. The Royal National Park platforms, the Illawarra ledges and the headlands south of Kiama are where 2 to 3 m of south swell does the real damage.

Marine Area Command is blunt about staying off exposed platforms while the warning is current, and the platforms near Sydney are the ones with the worst record.

Tides matter. The same 3 m swell on a high tide reaches much further up the platforms and sea walls than it does three hours either side.

Check the tide times for your own stretch of coast at Seabreeze NSW tides before planning a rock session or a bar crossing.

Divers. Expect heavy surge and shifting sand through Thursday, with visibility likely to be poor on anything facing south or south-east.

Sheltered northern-side sites will hold up better, but the entries and exits are the risk on a day like this rather than the dive itself.

Kiters and windsurfers. Wednesday afternoon has the pressure with a strong southerly and a rising sea, although it will be onshore and messy at most south-facing spots.

Thursday eases back and Friday goes light and variable, so the usable window is short and it sits mostly today.

South Coast context. The Eden Coast has a Gale Warning current today as the front pushes through the far south, which is a separate warning to the hazardous surf notice.

The Batemans Coast sits inside the hazardous surf warning for both Thursday and Friday.

Into the weekend. A high moves into the Tasman by the weekend, winds ease off and the leftover swell keeps dropping away through Friday and Saturday.

The point worth repeating is that the high eases the wind, not the water, so treat Friday as a swell day with nice weather sitting over the top of it.

Keep an eye on the current list at NSW warnings , because the coastal waters forecasts are reissued through the day.