Severe Tropical Cyclone Oma could cross the southern Queensland coast within days after changing direction overnight and continuing to move closer to the Australian mainland, the Bureau of Meteorology (BOM) says.
Beach swells are continuing to build and will remain large for several days, with winds expected to increase significantly along the southern Queensland coast from Thursday night.
"Currently, we expect Cyclone Oma to move south-west, and then a ridge to the south steers it back to the Queensland coast and may even bring it to a coastal crossing," forecaster Lauren Pattie said on Wednesday afternoon.
"Early next week, we could see Oma cross the coast or move in a more north-westerly direction parallel to the coast."
That could happen anywhere south from central Queensland to the New South Wales border.
At 11:00pm on Wednesday, the category two system was about 990 kilometres north-east of Brisbane, sitting off New Caledonia, where it caused some coastal damage and flooding.
"We can expect to see waves of 4 to 6 metres on some of the beaches as well. That swell won't abate until next week," Ms Pattie said.
"We expect to issue tropical cyclone watches within the next 24 hours."
A flood watch is current for catchments from south of Gladstone to the NSW border.
"The closer she comes to the coast, the more significant that rainfall will be and the further inland it will push," Ms Pattie said.
"We are expecting rainfall totals of between 100 and 200 millimetres per day from Saturday - isolated falls could be a lot heavier than that.
"The most likely region for that rainfall is the Sunshine Coast and Wide Bay."
Ms Pattie said it was rare for cyclones to cross the coast so far south.
"It is unusual to have a tropical cyclone this far south, however it is not unprecedented," she said.
"In 1990, [with] Tropical Cyclone Nancy, we had a watch out for the south-east coast. We also often see impacts from ex-tropical cyclones.
"It is because we have a number of other weather systems and these other weather systems are influencing what happens to Tropical Cyclone Oma, so they can be a little stronger or weaker and have a big difference on where exactly she goes."
BOM has also warned that abnormally high tides and dangerous surf conditions are expected along the Queensland coast from the town of 1770 to Coolangatta in the coming days.
It said dangerous surf conditions would develop on Thursday afternoon in the Fraser Island and Capricornia areas.
"These conditions are then expected to extend south over remaining south-eastern Queensland coastal waters during Friday," BOM said.
"Beach erosion is likely to continue with the hazardous marine conditions."
Tuesday's king tide along coastal areas north of Mackay caused some erosion at Midge Point and the Pioneer River to flow into the nearby carpark.
Wednesday's high tide was forecast to exceed the highest tide of the year by around half a metre.
Water Police Senior Sergeant David Edden said people should avoid any type of boating and water activities near surf-exposed areas for at least the next five days.
"All boaties, fishers, surfers and swimmers should reconsider any plans which involve the surf over the coming days," he said.
"It is also vital to check the security of your anchored vessel and ensure it is prepared for extreme winds and damaging swell.
"Those already on the water should ensure they are carrying the appropriate safety equipment and are wearing lifejackets.
"[They should] remember to log on with their local radio base and consider their safety management plan."
Gold Coast lifeguards are expected to close beaches as the swell increases.
Fencing has been removed from some Gold Coast beaches and the city's council has heavy machinery on standby to reprofile beaches and move sand to vulnerable locations.
On the Sunshine Coast, Mooloolaba's fishing fleet has largely returned home ahead of the system.
Mooloolah River Fisheries general manager Daryn Logan said only the bigger tuna boats and trawlers remained at sea and they were expected home within a day.
"At the moment it's totally unpredictable, so as soon as they know where that's gone or what it's doing, they'll get out there," Mr Logan said.
"In the meantime, the fishing grounds just get a bit of a forced rest."
Bargara surfing instructor Keith Drinkwater said conditions would be assessed daily but classes were likely to be cancelled for the rest of the week.
"A lot of sand erosion is going to occur but we just hope there's no damage, but nature takes its own course," he said.
"We have some classes booked every day but we've been very careful with what we do at the moment.
"It could be fantastic for surfers over the next three or four days.
"I'd hate to see learners and intermediate surfers go out there … you've got to be able to surf in your own means."
Will Cyclone Oma reach New Zealand?
MetService says while there is uncertainty around the exact track the cyclone will take, regardless, New Zealand will see significant weather this weekend, with warm moist air likely to push down over the North Island and interact with cold air from the South Tasman sea low. Weather events like this usually bring strong winds, heavy rain and even snow along the Southern Alps.
- ABC / RNZ