The remnants of Cyclone Evan will deliver a tropical Christmas to the North Island, while the South Island will bask in dry festive heat, forecasters say.

The moist and humid air, draped across the north, will continue to linger until Boxing Day.

A severe weather warning is in place for Northland for the rest of today. Since yesterday, 25-50mm of rain had fallen in Northland, and between noon and 9pm today another 50-80mm was expected.

"If you're in Northland, please stay up-to-date with any advice from Northland Regional Council and Far North District Council about local conditions, and what the New Zealand Transport Agency is saying about local roads,'' said MetService Chief Forecaster Peter Kreft.


Weather watches remain in force for northern parts of Auckland and Coromandel.

"While rain continues in Coromandel and northern Auckland, we've downgraded these areas to a Severe Weather Watch,'' said Mr Kreft.

"At this point, expected rainfall totals are not large enough to warrant a Warning. The north of the Gisborne district is still on Watch for rainfall too.''

The "very warm, humid and muggy'' low pressure will bring patchy showers for regions across the North Island, said MetService duty forecaster John Law.

Hawke's Bay and Gisborne will dawn cloudy tomorrow but it should clear into a fine day, with Napier reaching the high 20s (Celsius).

Wanganui should set the North Island's top Christmas Day temperature of around 30 degrees.

The high temperatures will also generate showers, possibly even thunderstorms for Taranaki, Wanganui, Manawatu, and Wellington.

While the low pressure is moving to the west of New Zealand, it will return again on Boxing Day, Mr Law said, bringing more ``cloudy, moist, and humid air'' for the North, with more showers.

The South Island can look forward to a mainly dry Christmas and Boxing Day.

Low cloud being pushed in from the Pacific Ocean could being early morning cloud for the east coast, but that should clear by the afternoon.

Central Otago will again boast the highest temperatures, with Alexander expected to reach 33 degrees Celsius.

Showers could develop tomorrow across inland parts of Nelson, Buller, and Marlborough, with rain also expected in the Canterbury high country, and foothills of Rangitata.

Boxing Day will see scattered showers across the South Island, but Mr Law said temperatures will remain high.

"It's going to be perfect BBQ weather,'' said fellow MetService forecaster Brooke Lockhart.