Weather: 'Atmospheric river' bringing monster storm to New Zealand this week

Heavy rain and freezing wind are set to batter the South Island this week as summer comes to a close.

An "atmospheric river" of pressure, left over from Australia's cyclones will make its way across to Tasman Sea, and hit the South Island on Monday, reports NIWA.

Due to this 'river', the West Coast will see an "exceptional" amount of rain on Monday and Tuesday, Metservice predicts. Flooding, slips, high river flows and washed out roads will accompany this heavy rain.

Experts are warning residents to be wary of the conditions that accompany this wild weather. Metservice meteorologist Andy Best warns it may lead to flooding and slips.

Canterbury and Buller are under a heavy rain watch, and the possibility of thunderstorms has not been ruled out by Metservice.

But it's not just rain; on Tuesday, a strong north-westerly front will hit southern New Zealand, having made its way across the Tasman Sea.

This front will bring cooler weather, as well as gales.

Canterbury, Otago, Fiordland and Marlborough are all on heavy wind watch, with warnings of "severe" gales throughout the day.

The front is expected to move over the island on Wednesday and in its wake, a much cooler southwest wind.

Friday morning is colder still. Earlier risers will be treated to dawn temperatures hovering around 6degC.

While the South Island freezes, the North Island is forecast to remain relatively pleasant. A persistent northerly flow is keeping Auckland temperatures between 24 and 25degC.

However, WeatherWatch is warning next week could be another chilly one, as the remnants of Cyclone Trevor joins forces with a cold front making its way across the Tasman Sea.

The front and the cyclone will likely bring rain across the North Island.