Wild weather's dangerous punch

02:17, Jan 09 2013
DOWNPOUR: Rain hits Fiordland, the Southern Alps and Dunedin in this MetService rain radar image from 1.05pm.
DOWNPOUR: Rain hits Fiordland, the Southern Alps and Dunedin in this MetService rain radar image from 1.05pm.

Severe weather warnings have been upgraded as heavy rain begins to pelt the South Island and MetService warns of wind gusts up to 150kmh.

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It says intense rainfall in the South Island could cause slips and rivers and streams will rise rapidly, while wind gusts of up to 140kmh in Wellington and 150kmh in inland Canterbury have the potential to uproot trees and bring down power lines.

Milford track has already been closed, after the Clinton River burst its banks and forced a tramping party to turn back when they reached waist-deep flood waters.

A front which has intensified over the Tasman Sea as it heads to New Zealand has prompted the warning for heavy rain in the west and south of the South Island and northwest gales in eastern areas, from Taranaki to Otago.

The front is expected to move across the South Island today.

By late this afternoon, winds in Wellington and as far north as New Plymouth should have picked up to maximum speeds.

Severe weather forecaster Erik Brenstrum said the front would most likely weaken significantly by the time it reached the North Island.

"There's already been heavy rain in and around Milford. Rain has also begun to reach Hokitika.

"It's unfolding the way we expected it to, so people in those areas that are affected by the rising river levels and rain falling on the Alps need to be very careful," he said.

According to the Department of Conservation, 85mm of rain has fallen in the Arthur Valley in the 5 hours up to 10am with a further up to 200mm forecast.

Spokeswoman Annie Wallace said a number of tramping parties were in the Milford Sound but had reached safety.

"A storm warning came in yesterday, with the event expected to peak this afternoon. Trampers on the Milford Track are safe and well with most trampers from Dumpling Hut proceeding off the track today before water levels peak and other trampers remaining at the huts a second night," she said.

Ultimate Hikes, who give guided tours in the Milford area, have been pulling trampers to safety using a helicopter.

DOC was advising all people in the area to know their limits and stay clear of swollen rivers.

It was estimated 120 independent walkers were currently on the Milford Track across three huts and 31 were expected to leave the track today.

Although the rain was expected to weaken by the time the front reached the North Island, wind gusts from Wellington to Taranaki should remain strong, Brenstrum said.

"It's the gap between the South and North Island that we often have to contend with - the wind rushes through there very fast."

People planning tramping or other outdoor activities in these areas should reconsider their plans as expected rainfall and wind gusts could be strong enough to make even driving hazardous.

An estimated 300-400 millimetres of rain was expected in Westland in the next 27 hours.

Heavy rain was also expected in Fiordland and the headwaters of the Otago and Canterbury lakes and rivers.

MetService also expects northwesterly winds to reach severe gale strength in Otago, Canterbury, Marlborough and Wairarapa, while northerly winds could reach severe gales in parts of Westland and northern Fiordland.

There was also a moderate risk of thunderstorms in Fiordland this afternoon and in northern Westland and Buller tonight.

There was a high risk of thunderstorms in southern and central parts of Westland and the Southern Alps from this afternoon into the evening.

Any thunderstorms were likely to boost local rainfall rates up to 25mm an hour or more.