Violent thunderstorms are lashing the country with torrential rain and flash flooding for the fourth day in a row.

MetService issued a severe thunderstorm warning for inland areas of the mid and bottom of the North Island and the upper South Island.


Today's thunderstorms are expected to bring heavy localised deluges with large hail stones. Some storms are expected to be so intense, up to 40mm of rain could fall in an hour sparking flash floods and slips, and driving could be hazardous.

The extreme weather will bombard the country from lunch time and will last until this evening.

Advertisement

Yesterday more than 10,000 lightning strikes were recorded over the country and severe thunderstorm cells sparked warnings for the Mackenzie Basin and Marlborough.

Meanwhile the mop-up is continuing in Roxburgh where SH8 is closed as road crews are clearing slips and repairing washouts on the main highway between Roxburgh dam and Millers Flat.

WeatherWatch.co.nz head weather analyst Philip Duncan said the daily thunderstorm pattern was more typical for the peak of summer, not spring. He explained that the thunderstorms occurred as easterly and westerly winds converged in the middle of the country. They typically start around lunch time, then peak from 3pm to 6pm in the North Island and 4pm to 7pm in the South Island due to their later sunset. The storms subside in the late evening.

"Then they'll pop back up again tomorrow morning like Groundhog Day.

"It's very unusual this pattern. It's not normal in spring to have long spells of warmer-than-average calm weather. This is very much like the peak of summer.

"The word normal shouldn't be used. This isn't normal weather I think it'll break quite a few records."

Duncan said some areas would get up to 50mm of rain today and parts of the central plateau would see a month's worth of rain this week.

The thunderstorms are set to continue through until Saturday when a strong westerly will dominate the country. The South Island will clear up on Saturday and the whole country will be clear on Sunday.

Fine weather would bring some relief next week except for a small sub-tropical low potentially brushing northern New Zealand, Duncan said.

But mid to late December looked more like spring with downpours and rain expected to be brought in by a front currently traversing Australia.

Today's severe weather warning affected Dannevirke, Hawke's Bay, Taranaki, Taihape, Wanganui, Manawatu, Tararua, Kapiti-Horowhenua, Wairarapa, Marlborough, Nelson and Canterbury High Country.

The Ministry of Civil Defence and Emergency Management advises that as storms approach people should:

​•Take shelter, preferably indoors away from windows.
​•Avoid sheltering under trees, if outside.
​•Move cars under cover or away from trees.
​•Secure any loose objects around your property.
​•Check that drains and gutters are clear.
​•Be ready to slow down or stop if driving.

During and after the storm, you should also beware of fallen trees and power lines, avoid streams and drains as you could be swept away in flash flooding.

Main centre forecasts

Whangarei

Mainly fine, but a few afternoon​/​evening showers. Light winds and a high of 23°C.

Auckland
Sunny spells, chance shower. Light winds and sea breezes and a high of 23°C.

Hamilton
Partly cloudy. Showers from late morning. Possible thunderstorm. Light winds and a high of 23°C.

Tauranga
Partly cloudy. Showers, mainly from late morning. Chance thunderstorm. Light winds with a high of 21°C.

Wellington
Morning low cloud or fog, then fine. Light winds and a high of 20°C.

Christchurch
Morning and evening low cloud, otherwise fine. Northeasterly breezes developing and a high of 22°C.

Dunedin
Fine apart from low cloud morning and night. Northeasterly breezes developing and a high of 20°C.

Queenstown
Morning cloud clearing to fine, but chance afternoon shower. Light winds and a high of 24°C.​