Revellers who are planning to hit the beach or the backyard cricket pitch on Christmas Day have been urged to start the action early.
A burst of showers could hit Sydney from the early afternoon, starting in the west from about 1pm and the city from 3pm.
Weatherzone meteorologist Josh Fisher said a top of 25 degrees was forecast for Sydney on Christmas Day, which would dawn with mostly dry conditions.
"We're actually looking at mostly dry and partly cloudy skies for the morning and into the afternoon. But there's a chance we could see a few showers developing later into the afternoon and evening," he said.
"The advice is to go and have your BBQs and head to the beach earlier in the day."
Isolated showers are forecast across the north of NSW on Christmas Day, tending scattered in parts of the north-east, while it will be partly cloudy across the south of the state.
South-east to north-easterly winds are forecast near the coast, tending light and variable inland.
Mr Fisher said more rain was forecast for the start of the Sydney to Hobart Yacht Race on Boxing Day, when the weather is expected to reach a maximum of 27 degrees in Sydney.
"For the start of the race, our weather models are actually pretty divergent for Boxing Day onwards. They both do still show that Sydney will see scattered showers on Boxing Day. The conditions will be worse than what we see on Christmas Day, with more showers, potentially heavy at times, and easterly winds," he said.
"As they make their way further down the coast it looks like that system ... will move further off the coast, so they could just see the odd brief shower on the 27th of December as they make their way down. Winds will be turning more to the east, north-east direction which should help and provide faster conditions."
A top of 29 degrees and mostly dry conditions are forecast for the start of the Boxing Day Test in Melbourne, Mr Fisher said.
"There is the chance of a brief shower during the afternoon, but nothing to stop game play for very long, if anything at all. It will be very isolated and brief," he said.
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