Northwest gales are expected to lash central New Zealand tonight and tomorrow morning, the MetService said today.

The strongest winds were expected about Wairarapa, Wellington and Marlborough and a warning was in force for those areas, said forecaster Andy Downs. A watch would be maintained for exposed inland parts of North Canterbury.

Mr Downs said another active front was expected to cross southern and central parts of New Zealand late today and tomorrow morning, bringing heavy rain and isolated thunderstorms to western and northern parts of the South Island.

"The heaviest falls are expected about the ranges from Fiordland up to northwest Nelson, also the Richmond Range, Marlborough Sounds and Tararua Range, where rainfall amounts could approach warning criteria in one or two places," he said.

"However, given the recent significant rain in these areas, these additional falls could still cause rivers and streams to rise quickly and there is a possibility of localised surface flooding and slips."

There was also likely to be brief period of heavy rain about Mt Taranaki and the hill country extending inland to Mt Ruapehu, including the headwaters of the Whanganui River tomorrow.

Another front embedded in a strong west to southwest flow was expected to cross much of the South Island tomorrow afternoon and evening.

"Squally showers and thunderstorms are likely to accompany this front and may bring potentially damaging gusts to parts of the West Coast and also coastal parts of Southland and Clutha," Mr Downs said.

Snow showers were likely down to 300 metres in parts of Fiordland, Southland and southern Otago, mainly the Clutha District, late tomorrow.

Although the amounts of snow were not expected to reach warning criteria, Mr Downs said significant accumulations were possible above 500 metres.

"These snowfalls are likely to affect some of the higher South Island passes, such as the Milford Road, and possibly the Lindis Pass and Arthurs Pass. Also, strong to gale winds over coastal hills are likely to make for bitterly cold conditions, which could put stress on vulnerable livestock," he said.

Another significant cold snap was likely on Tuesday, Mr Downs said. said there would be a rough few days ahead with severe gales, turbulent flights, thunderstorms, squalls and even tornadoes.

The onslaught would be mainly in the west with strong winds roaring around a large high over southern Australia and deep lows in the South Ocean.

"New Zealand is smack bang in the middle of this squash zone," said weather analyst Philip Duncan.

"We are in for several very windy days with west to south west winds, a drop in temperatures and the chance of thunderstorms, squalls and even a few tornados."