The nasty band of thunderstorms that swept over the country are expected to ease for most places today - although western areas should brace themselves for more of the same.

A low-pressure system so big it would engulf Australia is sitting over New Zealand and bringing with it tumultuous conditions.

MetService meteorologist Peter Little said a westerly flow would cause unsettled weather, with heavy showers and thunderstorms for some western regions in both islands.

"There will be a moderate risk for central parts of New Zealand and the west, and in the afternoon there's still a moderate risk there, and a low risk surrounding that area."

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A severe-weather rain warning remains in place for Eastern Bay of Plenty, Mt Taranaki, the Tararua Ranges and Buller.

The rest of the country could expect showers.

Snow was forecast in the far south falling down to 900m in the Central Otago high country.

WeatherWatch's Philip Duncan said the massive low-pressure system was the reason for the extended stretch of turbulent conditions.

"While bigger doesn't always mean more aggressive, it does explain why the nation is experiencing scattered rough weather and why this has been going on for five days now," he said.

Outlook for today

• Auckland:

Showers, possibly heavy from late morning and fresh westerlies. High 18

• Tauranga:

Cloudy and shower mainly in the afternoon. Gusty westerlies. High 17

• Wellington:

Mainly fine with midday showers. Gusty northwesterlies. High 16

• Christchurch:

Morning showers becoming fine. Southwesterly winds. High 14

• Dunedin:

Cloudy and showers. Southwestery winds. High 11