The weakening of the system came after it intensified overnight to a category 2.

The Bureau of Meteorology tracked the cyclone about 11am over the southern Coral Sea, about 810 kilometres east of Brisbane.

The weather bureau expected it to turn to the east on Saturday before heading north on Sunday, and then moving north-west by the end of the week.

Mooloolaba and off Point Lookout on the Sunshine Coast recorded maximum wave heights of 12 to 13 metres on Friday.

This was higher than wave heights recorded during Cyclone Oswald.

BOM meteorologist Michael Knepp said the ex-tropical cyclone was moving away from Queensland but weather warnings would remain in place for the next few days before it settled next week.

"She's heading away from Queensland right now and starting to turn back to the north and move north-west," he said.

"She will remain offshore in a weakening trend."

Mr Knepp said it was possible Oma could approach the north Queensland coast, which may bring rain to already drenched areas of the state.

"It might bring some rain but that will be highly dependent on the movement of the ex-tropical cyclone," he said.

"If it remains off-shore it remains more than likely none of that rain will make it to shore."

People on the south-east Queensland coast and islands were being warned to brace themselves for abnormally high tides, dangerous surf and damaging winds.

"Dangerous surf conditions are occurring about exposed beaches along the southeast Queensland coast south of Sandy Cape, including the Sunshine Coast and Gold Coast," a BOM spokesman said.

"These conditions are expected to continue on Sunday."

The spokesman said that, as water levels rose, there was a potential for significant beach erosion due to the conditions, which would also bring gale-force winds to Queensland.

"Locally, damaging wind gusts in excess of 90km/h are likely about the exposed coast and islands between Sandy Cape and the Queensland-NSW border today," he said.

"These damaging wind gusts may extend to the southern border ranges, inland to about Springbrook and Tamborine Mountain, today and into Sunday."

Locations that may be affected include Gold Coast, Maroochydore, Moreton Island, North Stradbroke Island, Noosa Heads, Caloundra, Rainbow Beach, Fraser Island, Tamborine Mountain and Springbrook.

Wind gusts of 96km/h were recorded at Cape Moreton on Moreton Island about 3pm on Saturday.

A hazard surf warning was also in place for Fraser Island Coast, Sunshine Coast, Moreton Bay and Gold Coast.

All 34 beaches on the Gold Coast will remain closed this weekend due to dangerous conditions.

Gold Coast mayor Tom Tate said Oma was still very unpredictable.

“Oma swell is bigger than that of [Tropical Cyclone] Debbie, the surf is still very dangerous as you can see out there and my attitude is that the warning has been issued, the beaches are closed, the sea wall at The Spit is closed,” he said.

“Anyone who jumps the fence, I spoke with the police, they can be prosecuted because they’re putting other people’s lives in danger if they get washed into the water, rescuers have to go in there.”

On Saturday, cars flooded by waves as ex-tropical cyclone Oma swallowed the Currumbin Surf Club car park.

Lifesavers conducted 16 rescues across Queensland on Saturday, with all patients outside the flags.

Surf Life Saving Queensland Gold Coast duty officer Sue Neil said eight people were asked to leave Gold Coast beaches because of the dangerous conditions during the dawn patrols.

"The conditions are still bad. We're seeing about 300 metres of white turbulent water and up to three-metre waves with an outgoing tide," she said.

"It is slightly better than this morning's incoming tide because it was looking quite dangerous.

"The surging waves were heading up and over the sand dunes even though we only had a 1.63-metre high tide at 11am.

"No one could even walk on the beach because there was no beach left and all the beaches remain closed and will stay that way throughout the weekend."

Ms Neil said the decision would be reviewed on Sunday morning.

"We do get these conditions from time to time and on several occasions all beaches had been closed for one or three days in a row," she said.

"It's prioritising safety and it's not worth people going into the water in unpleasant conditions, getting into trouble and putting lifesavers at risk who have to go out and rescue them."

The passenger ferry to North Stradbroke Island was cancelled this weekend, while the vehicle ferry will run two services on Saturday to clear the backlog of customers impacted by cancelled ferries.

- with Felicity Caldwell