"We've got you a nice anti-cyclone for Christmas," said MetService meteorologist Daniel Corbett.
He said there might be the odd thunderstorm or heavy shower in inland parts of both islands this afternoon.
WeatherWatch said there was a 70 per cent chance of heavy showers in many inland areas today, especially near the ranges.
The downpours could lead to flooding, but this was likely to be localised, WeatherWatch said.
In the North Island, the hot spots for thunderstorms were around the Central Plateau, spreading north to Waikato and the Auckland ranges.
But the wet weather will run out by Sunday.
Mr Corbett said there might be a few bursts of rain in a few places, but mostly it would be fine.
"There's just a few nibbles of moisture letting some showers to pop up - but not the ones where you'd say, 'Oh, the barbecue's off, let's all go inside'. It'll just be those quick little showers."
A large high over New Zealand was stopping "any nasty weather systems" from getting through, Mr Corbett said.
"Pack your sandwiches or whatever and head to the beach or the campground and find some shade.
"If you're unlucky, you might see a very quick shower, but it should be a lovely Christmas Day."
