Rough weather moves in; report of a West Coast tornado

[Te Puke Weather]

UPDATED 8:58pm --- A report has come in of a tornado near Hokitika on the West Coast.  WeatherWatch.co.nz reader and weather enthusiast Dale Small says he's heard reports of a tornado this evening.  "Been a pretty wild couple of hours here with some very big thundersqualls coming through. Especially hard down in the Hokitika direction with a roof being removed from a house somewhere in town, and now reports of a tornado which has thrown trees onto powerlines & "relocated livestock".. no further information on the latter but it certainly would not surprise me".

Across the weekend WeatherWatch.co.nz has warned of the risk of small scale tornados as the first Autumn storm of the year brushes past New Zealand.  The centre of the low is well south of the country but it's size means the South Island and lower North Island are in the path of gales, heavy rain and thunderstorms and on the West Coast the risk of isolated damaging squalls with weak tornados.

As of 8:55pm WeatherWatch.co.nz hadn't confirmed if the reported damage was related to a tornado or squall.

Earlier update 2:30pm

Some have sun, others wind and rain as a large storm well to the south of the country starts to affect the weather across New Zealand - especially the lower two thirds of the nation.  The rough weather is expected to mainly affect national parks and rural areas but some main centres are also in the firing line (see below for more details).

The cold change has already reached Southland with Deep South Weather reporting that Invercargill reached 16 degrees at 11am but is now at just nine, dropping over two degrees in the last hour alone - normally the warmest time of the day.

WeatherWatch.co.nz says the fronts are heading north and Queenstown has gone from 20 degrees at noon to just 12 degrees at 2:30pm.

A warm northerly is still blowing through Dunedin and right across Canterbury.  Christchurch residents are reporting mostly sunny weather with a north west arch appearing in the sky.  However colder, wetter, weather will move into Dunedin this afternoon and Canterbury tonight.

Rain is also moving up the West Coast with WeatherWatch.co.nz saying the more wintry, squally, conditions are not likely to arrive until this evening in Southland and the West Coast.

Head weather analyst Philip Duncan says the squally showers could bring hail, thunder and even localised damaging winds to the West Coast while squally showers with hail and possibly thunder are likely for Southland overnight.

For the North Island the windier, colder, weather isn't expected to arrive until Monday.



Earlier story from 9:40am Sunday

WeatherWatch.co.nz says the large low is showing up clearly on satellite imagery to the south and south west of the South Island with the main fronts now arriving in the deep south west.

The public owned forecaster, MetService, has issued several warnings - they include heavy rain warnings for much of the West Coast, and spillover into east coast waterways along with severe gales of up to 130km/h in places like Wairarapa, Wellington, Marlborough and Canterbury.

On top of the warning, WeatherWatch.co.nz forecasters say other severe weather is also possible with thunderstorms likely on the West Coast of the South Island today - and into the west coast of the North Island overnight tonight and tomorrow - and they bring another set of weather.

Head weather analyst Philip Duncan says latest satellite imagery at WeatherWatch.co.nz clearly shows the squally showers building to the south west of New Zealand.  "This is a significant storm and while the centre of the low won't actually come near New Zealand it is large enough to push gales, heavy rain and potentially damaging squalls up the South Island and lower North Island today".

"Some of the squalls for western areas of the South Island could produce damaging winds, hail storms, thunder and even the chance of a tornado being whipped up".

Mr Duncan says the West Coast is no stranger to these conditions and neither is the east coast - and that usually limits damage with trees in the east growing on a angle to withstand the winds and waterways in the west used to sudden downpours.  However Mr Duncan says the predicted wind speeds are high enough to uproot trees, break branches, lift roofing iron and making driving extreme difficult.  The rain is also heavy enough to spillover into the east coast waterways - causing rivers in places like Canterbury to rise without warning even if conditions are dry locally.

WeatherWatch.co.nz says the pressure gradient is significant (50 to 60 hPa) between the centre of a high to the north of the country and the deep low well to the south - that means strong winds for the country, mainly the South Island and lower North Island'.

WeatherWatch.co.nz says this is typical Autumn weather but will certainly contrast significantly with the recent settled conditions.  "We'll have heavy snow for parts of the Southern Alps, squalls with thunder on the West Coast, heavy rain for the West Coast and gales for eastern areas of both islands, especially the lower North Island - that's the extreme weather for the next 24 hours".

Map: Sunday afternoon wind map (red and orange indicates strong to gale force, yellow moderate, blue is light winds / weathermap.co.nz

Mr Duncan says the bulk of the severe weather will be in rural areas and national parks - with the worst of the weather mostly taking aim at the south west corner of the South Island and the West Coast.  "Certainly West Coast centres will see some rough weather today and those winds will howl through central New Zealand as the day wears on".

WeatherWatch.co.nz says the rough weather will build over the South Island throughout Sunday and develop over the lower North Island into the afternoon.  The upper North Island should start off fairly settled with cloudy periods and only a low risk of a remaining shower or two.  By the end of the day and overnight the main front will push into the rest of the North Island with winds continuing to build.

Windy and showery weather is predicted for many areas on Monday then should ease on Tuesday.

Another high is predicted to return to the country mid way through next week and last until Saturday.

Map: Where the bulk of the rain will be Sunday afternoon, orange, yellow and blue indicates the heavier rain, purple/pink indicates showers / weathermap.co.nz

WeatherWatch.co.nz says models indicate a large low with sub-tropical connections will move into the Tasman Sea for next weekend - it's too early to know what impacts it will have on the nation, we'll have a better idea in the next day or two.

www.weatherwatch.co.nz

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[TokWW]

Much of what I forecasted earlier in the week is unfolding...

Saturday will see strong West to Sou-West winds over the whole country with further spells of cloud and damp weather over most of NZ.  The winds will turn more southerly over the South Island and temperatures will drop. The winds again will be strong to gale force in Cook strait, possibly turning more Nor-Westerly through there.

Sunday will have a similar forecast again but the winds will be stronger to Storm Force along the Fiordland and Southland Coasts. Heavy bands of rain will pass in cold fronts up over the South Island during the day with some passing over the North Island too, with more Westerly winds, gale force around Taranaki.  Northland may get an evening cold front passing over with rain. The West Coast will receive very heavy rainfall amounts south of Westport.

Monday will see clearing weather in the North Island with Sou-Westers and still showers over much of the South Island with cold, strong southerly winds.

It seems it may not be clearing just yet in the North Island with chances of more rain on the west coasts of NI from an arch of a cold front from Queensland as a swooping cold front comes up the country and the Tasman dragging the rain in with it. 

WXSIM Forecast for Sth Waikato has mainly cloudy day with no rain tomorrow.