Rain and thunderstorms are lashing the country tonight - with downpours, chilly temperatures and showers set to continue until the end of the week.

A severe thunderstorm watch is in place for the upper half of the North Island this afternoon. Heavy rain, showers, strong winds gusting to 100 km/h, hail and the risk of a small tornado were predicted.

There is also a possibility that a few of these thunderstorms could become severe, producing damaging winds of 110 km/h or stronger or a damaging tornado, MetService reported.

Wind gusts of this strength can cause structural damage, including trees and power lines, and make driving hazardous. If any tornadoes occur, they will only affect very localised areas.

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MetService meteorologist Josh Griffin said the Taranaki area had been hit with 100 lightning strokes in the last few hours.

We start the working week with a broad area of low pressure dominating our weather, but we can look forward to a brief...

Posted by MetService New Zealand on Saturday, 16 September 2017

A severe weather warning is out for Buller, Westland and the Canterbury Headwaters where between 50mm to 100mm of rain could fall over Sunday.

Tomorrow heavy rain should turn to showers that will affect most of the country, Griffin said.

Temperatures will plunge as the wind whips around to a more southerly direction. South Islanders would gets lows in the single digits and highs in the low teens, Griffin said.

"The North Island will have showers, possibly heavy falls gradually easing into the evening. The South Island is going to see rain developing on most of the east coast into the evening."

Scattered showers would pepper the country on Tuesday and further into the week, Griffin said.

"It looks like typical springtime weather. Closer to the end of the week it looks like it will still be a bit rainy."