Forecasters are calling the Christmas forecast "very lucky", for while it might not be the quintessential scorching hot Kiwi summer day, it could have been much worse.

After a week of rain and isolated showers across much of the country, MetService is now predicting a relatively settled Christmas Day for most places, although for some it might feel a little closer to winter than they'd like.

Tropical Cyclone Yasa, a former category 5 system that devastated parts of Fiji and killed four people, has now been downgraded to an ex-tropical cyclone as it moves south of Tonga.

At one stage it looked to be tracking for a direct hit over the North Island but, thanks to a mighty ridge of high pressure this week, the system has weakened substantially and any remnants are looking to track southeast of the country.

"We have been very lucky not to have a tropical cyclone hitting us over Christmas," MetService meteorologist Ashlee Parkes said.

"It is still active so it is difficult to track, but at this stage it appears to be moving southeast of the country."

However, two low-pressure systems are forecast to arrive in the coming days from across the Tasman Sea.

While they are not linked to Yasa, they will bring warm tropical air from the northwest, meaning plenty of moisture for the West Coast of the South Island.

Eastern parts of the North Island will be the hot spots, with mostly fine conditions and temperatures in the late 20s.

Parkes said the first low was due to bring rain on Monday to most of the South Island.

A heavy rain watch is in force today for Westland south of the Glaciers and Fiordland north of Milford Sound.

The North Island was looking fairly fine, with just some showers inland south of Waikato.

The low would continue over the rest of the country Tuesday, bringing scattered rain to both main islands.

The system would gradually clear Wednesday, with the North Island again looking good along with the South Island early, before another, deeper low arrived late bringing more rain to the West Coast and potentially spreading east into Canterbury.

Few spots around the country will look like this come Christmas Day, however, it could have been much worse. Photo / File

This would likely continue into Thursday, before clearing in the evening with a more settled southwest flow taking over.

"This will see isolated showers in western areas and fine but with cloudy periods in the east," Parkes said.

"It is not your classic Kiwi summer day, but it will be nicer than what we will be having at the start of this week."

On the big day Auckland would see fine spells and a high of 21C.

The best spots are looking to be the eastern areas of the North Island, with Tauranga and Napier both hitting highs of 25C and mostly fine weather.

The South Island meanwhile was looking a little worse off, taking more of the brunt of the cool southwest flow.

Christchurch would see a high of 18C, while Dunedin would only reach 16C with showers and Invercargill an even cooler 15C.

Christmas Day forecasts

Whangārei Fine spells. Southwesterlies easing. 24C high, 15C overnight.

Auckland Fine spells. Southwesterlies easing. 21C high, 15C overnight.

Hamilton Fine spells. Southwesterlies gradually dying out. 22C high, 10C overnight.

Tauranga Fine spells. Southwesterlies dying out in the morning. 25C high, 13C overnight.

New Plymouth Fine spells. Southwesterlies. 20C high, 11C overnight.

Rotorua Fine spells. Southwesterlies dying out in the morning. 23C high, 10C overnight.

Napier Cloudy periods. Southerlies gradually dying out. 25C high, 14C overnight.

Wellington​ Becoming fine. Southerlies dying out in the afternoon. 20C high, 11C overnight.

Nelson​ Becoming fine. Southwesterlies dying out. 22C high, 10C overnight.

Christchurch​ Cloudy periods. Northeasterlies developing. 18C high, 8C overnight.

Dunedin​ Cloudy periods. Showers from morning. Winds becoming light. 16C high, 8C overnight.