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An upper-level trough passed through the east coast on Thursday, causing rain to lash both states.

A low-pressure system developing over the Coral Sea is expected to bring increased showers for the NSW coastline, according to Weatherzone. On Friday, the weather service said the upper-level trough will move further east and cause the Coral Sea low to deepen off south-east Queensland.

Festival goers attending Splendour in the Grass in Byron Bay on the North Coast are advised to pack gumboots. Weatherzone forecasts up to 10 millimetres on Friday, following the 20 millimetres the region received on Thursday. Temperatures will stay below 20 degrees in Byron for the duration of the festival, topping out over the weekend at 18 degrees, according to predictions.

In Victoria, the weather is likely to remain dry until the weekend when a trough brings some rain over the state. Monday is likely to bring 5 to 10 millimetres of rain in Melbourne, with another 3 to 8 millimetres on Tuesday.

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A negative Indian Ocean Dipole is likely to occur in the next two weeks which would see above-average rainfall occur for much of Australia. Pippard said the warm waters off the northern shelf of Australia would bring more moisture and cold fronts across the majority of the country, bringing more rainfall.

Meanwhile, the Bureau of Meteorology remains on high alert for another La Nina to emerage, with a 50 per cent chance of a third one occurring this year.

It’s uncommon to have a three-year La Nina event, which has occurred only three times since the middle of the last century. Australia has experienced 19 La Nina events since 1900 and 13 have coincided with flooding in eastern states. The average rainfall from December to March in La Nina years is 20 per cent higher than the long-term average.

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