Low pressure bringing rough weather for some at the weekend

There will be unsettled and rainy weather for some this weekend. Photo / File

It's set to be a weekend of rough weather for some parts of the country, thanks to a low pressure system sweeping in from tomorrow.

The low is expected to deepen over the Tasman Sea on Friday before crossing the country on Saturday, with an associated active trough bringing a period of heavy rain to most of the North Island and upper South Island.

The heaviest falls were expected from around 6pm tomorrow through to Saturday morning over Mt Taranaki, Buller, Nelson and northern Marlborough, where between 80 to 100mm of rainfall was expected.

For Wellington and the Marlborough Sounds, northerly gales could become severe for a time on Saturday.

As the low moved to lie to the east of the South Island on Saturday, strong southerlies and rain were expected to spread along the east coast of the South Island.

Snow could also affect the higher South Island roads on Saturday - at this stage, the largest accumulations were expected to be in Canterbury, with heavy falls possible above about 800 metres.

WeatherWatch analyst Philip Duncan said the "incredibly fast development" of the low meant a rough weekend for some places.

"While a large low often means the rain clouds get fractured and broken up, the low has enough energy to bring localised flash flooding to some areas," he said.

Mr Duncan expected to see very wet easterlies into Otago and parts of Canterbury on Sunday, along with wet west to north west winds in the North Island.

"The flip side means the west of the South Island may be mostly dry on Sunday but heavy rain could still form over the dry eastern North Island as a colder southerly sweeps in," he said.

"Rain may also become heavy in Dunedin and coastal Otago this weekend - with set-in rain lasting a day or so those concerned with flooding may want to keep a close eye on the movements of this low."

Unsettled weather was likely to continue into early next week, with westerlies over the North Island and southerlies over the South Island and rain or showers for most places, the MetService reported.

Heavy rain warnings

• MT TARANAKI: Periods of heavy rain expected from tomorrow evening through to Saturday morning. In the 10 hours from 10pm tomorrow to 8am Saturday, expect 80 to 100mm to accumulate. Further rain is expected through the rest of Saturday and another 30 to 40mm may accumulate by midnight.
• RANGES OF WESTERN NELSON AND BULLER: Periods of heavy rain expected from tomorrow evening through to Saturday morning. In the 15 hours from 6pm tomorrow to 9am Saturday, expect 100 to 140mm to accumulate. Further rain is expected through the rest of Saturday and another 30mm may accumulate by midnight.
• RICHMOND AND BRYANT RANGES: Periods of heavy rain expected from late tomorrow evening through to Saturday morning. In the 10 hours from 10pm Friday to 8am Saturday, expect 80 to 100mm to accumulate.