Weather: Severe thunderstorm warning for parts of North Island

MetService has issued an upgraded thunderstorm warning for Auckland and Waikato this evening.

An alert sent to mobiles phones warned MetService weather radar had detected severe thunderstorms near Auckland, Kumeu, Albany, Henderson, Manukau Heads, Whenuapai, Greenhithe, Coatesville, Paremoremo, Hobsonville, Massey, Te Atatu, Waitakere, Swanson, West Harbour, Glen Eden, Kelston, Ranui and North Harbour.

The warning — upgraded from the all-day weather watch issued this morning — said areas of Auckland and Waikato were likely to be affected by the thunderstorms until 7.15pm Sunday evening.

Earlier, MetService issued a severe thunderstorm watch for Northland, Auckland, Waikato, Waitomo and Taumarunui, following days of wild weather across parts of the North Island.

Ex-tropical Cyclone Tam and its associated troughs are expected to affect the country during Sunday and Monday, bringing heavy rain to parts of New Zealand.

In an update shortly after 8am, the forecaster warned a line of thunderstorms was expected to develop over southern Northland and Auckland this afternoon, and move slowly eastwards across the region.

It said the thunderstorms could produce localised heavy rain between midday and 8pm on Sunday, and some may be severe about southern Northland (south of Whangarei) and the broader Auckland region.

"Rainfall of this intensity can cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips,” MetService said.

Waikato, Waitomo, Taumarunui were also placed under a severe thunderstorm watch lasting nine hours from 1pm Sunday until 10pm Sunday.

MetService meteorologist Oscar Shiviti told 1News that rainfall rates of 25mm - 50mm per hour could be expected for some areas.

"Looking at the radar imagery doesn't look like in particularly any one spot where they are receiving constant heavy rainfall, so it was just consistent on and off showers for a lot of the regions," he said.

He said a severe thunderstorm watch issued yesterday for eastern Bay of Plenty and northern Gisborne/Tairawhiti has been lifted as thunderstorm activity was now expected to remain offshore.

Shiviti said "a lot of those thunderstorms that we were expecting in these areas actually have stayed offshore".

In an update shortly before 8am, Metservice gave a full overview of the updated watches and warnings.

Severe Thunderstorm Watch

Northland, Auckland - eight hours from midday Sunday until 8pm Sunday.

Waikato, Waitomo, Taumarunui - nine hours from 1pm Sunday until 10pm Sunday.

Heavy Rain Warning - Orange

Taranaki Mounga - 27 hours from 9pm Saturday until midnight Sunday.

Tasman northwest of Motueka - 24 hours from 6am Sunday until 6am Monday.

Heavy Rain Watch

Gisborne/Tairawhiti north of Tokomaru Bay, also Bay of Plenty northeast of Te Kaha - 13hrs from 11pm Sat, 19 Apr - noon Sun, 20 Apr

North Taranaki, excluding Taranaki Mounga - 13 hours from 9pm Saturday until 10am Sunday.

The Buller District and Nelson/Tasman about and southeast of Motueka, including the Bryant and Richmond ranges and the Rai Valley - 27 hours from 6am Sunday until 9am Monday.

North Canterbury about and north of the Waimakariri River, and Marlborough (excluding the Sounds, Richmond Range and Rai Valley) - 29 hours from 8am Sunday to 1pm Monday.

Ranges of the Westland District - 19 hours from 8pm Saturday until 3pm Sunday.