While WeatherWatch is predicting an "enormous storm" to hit the South next week, the MetService and Niwa are calling the forecast premature.

Philip Duncan of weatherwatch.co.nz, said the storm would bring with it a low air pressure system so deep it would be regarded as being associated with the "world’s largest storms".

The low pressure system would deepen over the Southern Tasman Sea and New Zealand area this weekend before smashing the South Island with an "Antarctic blast", he said.

Deep low pressure storms this size did occur in the Southern Ocean "from time to time in winter", but this one was different as it was forming in the New Zealand area and then scheduled to rapidly deepen in the Southern Ocean on Sunday and Monday.

"The incoming low is significant and will produce severe weather and is forecast to have very low air pressure, potentially into the 940hPa range which is right up there with some of the world’s largest storms.

"At this stage it looks as though the coldest portion of this weather will arrive next Monday, Tuesday and Wednesday, mostly over the South Island and lower North Island."

The storm would likely be centred south of the country.

It was too early to know which areas would be hardest hit, however the West Coast would be the target of heavy rain, he said.

"Then bitterly cold south to southwest winds up to gale force in exposed areas, as far north as Auckland possibly, and snow levels once again lowering to sea level in the south around Fiordland and maybe Southland and Otago too".

MetService meteorologist Andrew James said the prediction was premature.

The weather pattern was "quite typical", he said.

"The low that they are talking about is not especially low for the Southern Ocean."

MetService was focusing more on potential heavy rain throughout the country and strong northwest winds for the northern North Island across the weekend.

Next week was "quite far away".

"We’re not talking about that at the moment."

Niwa has also taken aim at the projection, calling for calm.

"Have you heard a report about a storm next week?" it wrote on Twitter. "At this point, there is no need to be alarmed.

"There's a good chance it could be really far south of New Zealand, sparing the country of major impacts."

But Weatherwatch.co.nz responded, tweeting, "You may not be interested in the well being of newborn livestock but we very much care and want to give farmers the best possible advanced warning. Queenstown has snow forecast, so too does Southland and we are in key lambing and calving season. NZ is different to America".

Meteorologist Ben Knoll, of Niwa, told the New Zealand Herald that as far as he was aware, the major lambing season kicked off in September.

He added that while there would be snow and rain with Monday's system, it would hit the usual high country areas and was not likely to be any bigger than what shook the country last weekend.

"Comparing the two I think that what we saw last week would have been a larger impact to the country on a whole, so that's where it stands right now, at least that's our opinion."

Mr Duncan today remained steadfast in his prediction and agreed that while it was winter and normal to get storms involving heavy rain and snow, this one was looking particularly nasty and people, particularly farmers, had a right to advanced knowledge.

With NZME