Heavy rain warnings for parts of South Island

An "atmospheric funnel" is bringing significant heavy rain and strong winds to much of the country today and into tomorrow.

Orange heavy rain warnings are in place for many areas of both main islands, and downpours were already hitting Auckland early this morning.

MetService said the severe weather was caused by a front moving eastwards, and was expected to last into Wednesday morning. It advised people to keep up to date with the latest warnings and watches.

Orange heavy rain warnings were in place for Auckland, Coromandel Peninsula, Bay of Plenty, Central North Island mountains, Taranaki Maunga, Tasman, Nelson, Marlborough, the Westland ranges, and at the headwaters of Canterbury and Otago lakes and rivers.

Some strong wind watches were also in place for parts of the North Island.

Weatherwatch's head forecaster Philip Duncan told First Up an "atmospheric funnel" had stretched right across the South Pacific.

"When you look at the rain map that covers the South Pacific, you see what looks like a funnel that goes from Vanuatu to Fiji to Tonga and it comes straight down in a v shape and points to the top of New Zealand and the top of the South Island.

"It's not necessarily the biggest rain band in the world, but the fact that it is being funnelled into one point or some narrow points means that we are going to get some very heavy rain stuck in some places like the top of the North Island, the top of the South Island and the West Coast."

Duncan said the top of both Islands were the biggest concern because they "don't normally get a month of rainfall in a day".

He said wind was also set to hit, and power cuts were likely in some places.

"It's pretty widespread but - again it's that tunnel shape - most of the worst of that wind is at the top of New Zealand.

"Really the worst of the winds look to be around Auckland, Northland, Coromandel Peninsula, and my hometown of Te Aroha in the eastern Waikato."

The worst of the weather was expected today, he said.

Tasman Mayor Tim King said the district was well-prepared, just over two weeks after the last flood caused widespread damage there.

Nelson-Tasman Civil Defence is being bolstered by emergency managers from across the country as the battered region endures another deluge.

Up to 180mm is expected to fall across Tasman west of Motueka, and the heaviest downpours are expected between mid-morning and early afternoon.

Civil Defence's Emergency Operations Centre is fully staffed and will be open from 7am.