Whole South Island, parts of North Island on watch for storm

Wednesday, 31 January 2018

The entire South Island is subject to weather warnings and alerts for Thursday, as a storm bringing heavy rain and severe gales approaches.

Combined with high tides, the low that was Tropical Cyclone Fehi could see parts of the South Island inundated with water when it hits, MetService says.

The low was in the northern Tasman Sea early on Wednesday, heading south and will pass to the west of most of New Zealand. It is expected to start crossing the south of the country on Thursday.

The area expected to get the heaviest rain was in Westland south of Otira, where up to 400mm could fall in 36 hours from 9pm Wednesday, with the most rain likely in the ranges. Nearly 200mm of rain could fall on the town of Franz Josef in the 24 hours from 6pm Wednesday, a computer forecasting model suggested.

**READ MORE:

* South Island to swelter as temperatures soar past 30C

* Temperatures could go as high as 40C

* Scorchers to start the week, storms on the way**

Inundation along the West Coast of the South Island and Nelson could occur during Thursday.

The State Highway 6 stretch from south of Hokitika to the start of Haast Pass - which includes Franz Josef - looked likely to be the inhabited area that would get the most rain, MetService meteorologist Tui McInnes said.

Fehi was 'going to bring some severe weather to us, starting late tonight, in combination with a front coming from the Southern Ocean,' MetService meteorologist Karl Loots said.

Gales could become severe in Westland and Buller during Thursday, and turn from the northeast to the southwest during the day.

Most of the country was expected to get some rain on Thursday, apart from Gisborne, Christchurch and northern Canterbury.

A severe weather watch issued by MetService at noon on Wednesday identified the possibility of rainfall accumulation reaching warning amounts in Wellington, Horowhenua Kapiti Coast, Taranaki away from the mountain, Taihape, Taupo, Taumarunui and Waitomo including Tongariro National Park during Thursday.

Winds may also reach severe gale force in Canterbury Plains, Christchurch, Wanganui, Manawatu, Horowhenua Kapiti Coast, Wairarapa, Fiordland and eastern Otago on Thursday.

Some rain was expected to continue on Friday.

Severe Weather Warnings and Watches from today. For details, check here https://t.co/qHyE5zhh6X.

EDIT: to include Marlborough

^Tui pic.twitter.com/XWpEQjCNe9

— MetService (@MetService) January 30, 2018

WHAT WILL THE TEMPERATURES DO?

Temperatures would start dropping in some places on Thursday with Invercargill expecting a high of just 16C and Alexandra 21C.

But before then, Wednesday was going to be warm - Dunedin was forecast to get to 34 degrees Celsius on Wednesday.

The heat wouldn't reach the heights of Tuesday, when, Niwa Weather reported, Clyde got to 37.6C - New Zealand's hottest January temperature in 14 years.

'We do have this really sub tropical air mass being blown over the country in the northerlies ahead of the ex-tropical cyclone coming our way,' Loots said. 'So it will be hot and humid.'

For the rest of the country there's only a chance of a few showers on Wednesday and it will be warm again.

As well as the 34C expected in Dunedin, Invercargill was forecast to get to 30C, Christchurch to 33C, Alexandra 32C, Masterton 31C, and Napier 31C.

An extreme fire danger warning was in place for the Canterbury region, ECan said.

'For the next 48 hours, no permits will be issued by Fire and Emergency NZ for fires in Christchurch, Selwyn, Hurunui or Waimakariri districts,' it warned in a tweet.

THUNDERSTORMS

There was also a moderate risk of thunderstorms and localised downpours over northern and western parts of the North Island during the afternoon and evening on Thursday.

Any thunderstorms that occur are expected to produce heavy rain of 15 to 25mm per hour and possibly more. 

The localised downpours which could occurare expected to produce rates of 25 to 40mm per hour and possibly more.

Rainfall of that intensity could cause flash flooding, slips and hazardous driving conditions.

Additionally, there was also a moderate risk of thunderstorms with very heavy rain about northern Westland, Buller, Nelson and northern Marlborough during the afternoon and eastern parts of Taupo and Bay of Plenty in the evening.

A broader low risk of thunderstorms existed for the eastern North Island and upper South Island.