'Really messy' 18 hours ahead as rain bands move up NZ – MetService

A continuous stream of rainbands are sweeping north today, with thunderstorms expected to spread over "the entire western coastline of New Zealand".

MetService meteorologist Heather Keats told Breakfast she had "lost count of the number of fronts that are tracking up over the country today", and the heaviest falls would be in the west.

Waterspouts and small tornadoes possible as 'messy' fronts hit - watch on TVNZ+

"It's interesting with the thunderstorms because it's the entire western coastline of New Zealand, all the way up to Northland, and then on the screen we're looking at storm energy. So that's CAPE (Convective Available Potential Energy)," she explained.

"Basically it is the energy needed to fuel the thunderstorm. So it's showing nicely in the areas that are likely to see those thunderstorms.

"They're all along those coastlines over the next sort of 18 hours, and we're going to see possibly very strong wind gusts, but also the potential is there for waterspouts and small tornadoes," she added.

"They need quite specific ingredients, but they are there today, so it's one to watch."

She said this would be "an interesting day of weather".

"At the moment, the heaviest rain is sort of sitting over Buller and Nelson Lakes. We've had quite a few thunderstorms spark up already. We've had about 250 [lightning] strikes in the last 24 hours," she said.

"They're mostly offshore and sitting over sort of Fiordland, that sort of area of the west coast of the South Island. But they will spark up and continue to spark up today as those fronts track over the North Island."

Keats said the country would get "these really heavy rain bands moving up over the country, over the North Island tomorrow".

"At the moment, just one heavy rain watch [is] in place for the Tararua Ranges, and a couple of road snowfall warnings for Crown Range Rd and Milford Rd."

She said more watches and warnings were likely to be added later this morning.