Weekend weather: Warning for drivers as flooding closes roads in Haast

The West Coast and South Island headwaters will see "significant" rainfall this weekend, with orange heavy rain warnings in place until Saturday, MetService says.

Although much of New Zealand would experience warmer-than-usual temperatures over the coming days, a front would bring heavy rain to western and southern parts of the South Island, the forecaster said.

Westland's mayor said the district was prepared should heavy rain cause disruption and flooding.

Helen Lash said it had been raining steadily in the district on Friday, and there was already surface flooding in South Westland, with more rain forecast for the ranges overnight.

"Regional council river management staff are already in place in all the key areas in South Westland, police are now in place in all those towns in case they are needed. We are not waiting to see if we are going to end up with a Civil Defence situation - we are getting everybody on the ground."

Lash said organisations were keeping a close eye on the situation.

She was aware there were a number of people visiting the region who may not be familiar with the conditions.

"People from overseas aren't used to driving in these conditions, and you can come around a bend and then you've got a foot of water in front of you, and if you are travelling at speed, you can end up off the road.

"And we just ask as normal in these conditions that people drive with caution, and if you don't need to be out in the dark of night, on the roads if there is surface flooding, then they don't put themselves in that position."

Police said flooding had closed a number of roads in the Haast area on Friday night. They were asking people to be extra cautious.

Minister for Emergency Management Mark Mitchell said hydrologists were keeping a close eye on the Waiho River in Franz Josef as heavy rain continued to fall.

MetService had issued an orange rain warning for Westland, with the region forecast to get up to 400 millimetres of rain by noon Saturday.

Mitchell had travelled to the West Coast to visit Franz Josef to see how the Waiho River coped with the forecast deluge.

He said the river was the biggest area of concern.

It looked okay on Friday night, he said, but hydrologists were monitoring it as heavy rain was set to build.

Mitchell said Westland residents should stay off the roads unless it was absolutely necessary to travel.

Westland's emergency operations centre remained on standby.

Rain and wind across the motu

The following orange heavy rain warnings are in place:

• Grey and Buller Districts 1am-9pm Saturday; expect 100 to 130 mm of rain in the ranges, and lesser amounts about the coast. Peak rates of 15 to 25 mm/h about the ranges Saturday morning and afternoon.
• Westland, until 1pm Saturday; on top of what has fallen, expect 250 to 350 mm of rain about the ranges (possibly more in localised areas), and 100 to 130 mm nearer the coast (especially around the Glaciers). Peak rates of 25 to 35 mm/h expected about the ranges.
• Canterbury headwaters, south of Arthur's Pass from 9am Friday to 12pm Saturday; on top of what has fallen, expect 250 to 350 mm of rain about the main divide, and 150 to 200 mm within 15 km farther east. Peak rates of 25 to 35 mm/h expected about the divide.
• Otago headwaters until 6am Saturday; expect 80 to 140 mm of rain about the main divide, and 50 to 80 mm within 15 km farther east. Peak rates of 15 to 20 mm/h expected about the divide.
• Fiordland about and north of George Sound to 3am Saturday; expect 80 to 100 mm of rain, on top of what has fallen. Peak rates of 10 to 20 mm/h.

There is a moderate chance of upgrading to a red heavy rain warning for Westland, a low chance for Canterbury, and a minimal chance for Grey, Buller, Fiordland and Otago.

There is a strong wind watch from midnight Friday to noon Saturday for the Canterbury high country, where northwest winds may approach severe gale in exposed places.

Northwesterlies could also become severe in Wairarapa, Wellington and Marlborough, MetService said.

Elsewhere, warm temperatures will cover New Zealand, with fine, dry and warm conditions in the east and north, MetService said.

Temperatures in some places, such as Hawke's Bay, could reach 30 degrees Celsius.

On Saturday, the North Island would be partly cloudy with isolated showers, and rain developing in the southwest later. Apart from areas affected by heavy rain warnings, the South Island would see fine spells and isolated showers.

On Sunday, there would be rain in the west of the North Island, with heavy falls, and a few showers elsewhere. The South Island would see rain developing in the southwest and fine spells and isolated showers elsewhere.

Warmer than usual

MetService meteorologist Lewis Ferris said much of the country was already experiencing warm and humid conditions.

"That is going to help to drive this very heavy rain we are going to see along the West Coast of the South Island through the rest of Friday into Saturday.

"Some parts of the Westland Ranges might see up to 400 mm of rain in around 27 hours until midday on Saturday so it is going to be quite an intense bout of rain."

The wet weather would make its way across to the North Island on Sunday but it was not expected to be as heavy.

It comes as the country is experiencing warmer than usual temperatures, with hot air travelling across the Tasman from Australia.

"Some areas on the east coast of both the North and South Islands are beginning to get quite dry and we've had a run of warm temperatures that do look to extend into the weekend with the strong northwesterlies, which does bring an increased fire risk so people need to be a bit more careful."

West Coast Emergency Management manager Claire Brown said it's closely monitoring the severe weather forecast for Westland on Friday through to Saturday morning.

"It is not unusual for these areas to receive these amounts of rainfall, however as always, we need to be closely monitoring and ready to activate, if need be, particularly for the Westland district."

An agency briefing took place Friday morning to share information and planning arrangements. Community coordinators had been contacted and West Coast Emergency Management was working closely with partner agencies

People were being warned rivers may rise quickly, surface flooding and slips are possible and driving conditions could be hazardous.

Road closure

The Milford Sound Highway has been closed as a precaution over fears warm rain and melting snow could lead to end-of-season avalanches.

MetService and NZ Transport Agency / Waka Kotahi warned motorists around Clutha and Southland they may also strike very wet conditions on Friday afternoon.

NZTA system manager for the central South Island Mark Pinner said people should check its traffic pages before setting out, and be prepared to take a break if rain got hard and made visibility poor.

Highway crews were ready for the heavy rain and watching spots like Muddy Creek in Otago, State Highway 6, where slips have caused overflowing onto the highway in the past.

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