East coast surfers have defied warnings about large swells whipped up by ex-cyclone Oma, a sub-tropical system that intensified into a category two storm early on Saturday but was downgraded by 11am after taking a south-eastern turn.

The storm, twice the diameter of 2017’s deadly cyclone Debbie, was tracking south towards Lord Howe Island but was predicted to turn and head north again.

The Bureau of Meteorology said it was unpredictable but could re-intensify to category two as it sat about 800km off the coast of Brisbane.

Bureau of Meteorology, Queensland (@BOM_Qld) Oma is now a sub-tropical system in the southern Coral Sea, around 810 kilometres east of Brisbane. A Severe Weather Warning remains current for coastal areas south of Sandy Cape for damaging winds, abnormally high tides and dangerous surf. See https://t.co/0Wd6T18wPL pic.twitter.com/hhKUuVbyJc

The storm was moving slowly southeast on Saturday evening, and was expected to continue to bring abnormally high tides, damaging winds and large swells, causing beach erosion, and coinciding with king tides.

Ann Farrell, the New South Wales state manager for the Bureau of Meteorology, said they expected coastal inundation in low-lying parts of the affected areas.

The bureau warned of waves exceeding five metres between Coffs Harbour and the Queensland border. Wave heightsof up to 10 metres were recorded offshore at Byron Bay on Saturday.

Cyclone Oma eases but Queensland and NSW weather warnings remain Read more

A hazardous surf warning was in place for Saturday and Sunday for Fraser Island Coast, Sunshine Coast Waters, Moreton Bay and Gold Coast Waters.

Cape Byron received wind gusts of 95km/h on Saturday morning, as did Moreton Island, north-east of Brisbane.

The Queensland premier, Annastacia Palaszczuk, urged people on Friday not to go out into the surf, saying authorities were monitoring the storm and warning of the hazardous conditions on the beaches despite it getting weaker.

Phil Ayres, chief operating officer of Surf Life Saving NSW, said: “The message for beachgoers and locals is that if the flags are down, it’s not safe to swim.”

Luis Aleixo (@luis1aleixo) Caloundra - Kings Beach #RollingSurf from cyclone #Oma #CycloneOma pic.twitter.com/9P7ZqalW9a

Between Noosa and Mooloolaba, lifesavers rescued 43 surfers on Thursday, the ABC reported.

All Gold Coast beaches remained closed for swimming on Saturday, but the big waves lured surfers to take to the water in droves.

Mooloolaba received an offshore swell of up to 13 metres on Friday, and Coastalwatch crowed over a video of Kirra Beach showing Mick Fanning, Joel Parkinson, Mitch Parkinson and “many more core lords getting mega slotted”.

Noosa has “epic, perfect lines”, Coastalwatch said, but the site’s chief forecaster, Ben Macartney, warned that the potentially “historic event” for Queensland’s beaches included the capacity for large-scale erosion.

The big swell was expected to travel down the coast – Sydney was forecast to receive two-metre waves by Sunday, but surfing conditions were likely to be hampered by offshore winds.

As Oma eased and moved away from the Queensland coast, the threat of increased fires also reduced. The high fire-risk areas inland – which have received little rain in recent times – were not expected to have strong winds.

The state has had nine declared disasters this past summer, and the Courier Mail says almost two-thirds of local government areas have been affected.