Heavy downpours, strong winds forecast as wild weather looms

A large weather system is expected to bring heavy rain and strong winds to the upper North Island from today.

MetService has issued an updated range of heavy rain and strong wind warnings kicking in from this morning into Friday as Tropical Cyclone Tam was expected to transition into a deep subtropical low as it approaches the country from the northwest.

Northland is under an orange heavy rain warning until 9pm tomorrow, with 100 to 150mm of rain expected. There is also an orange strong wind warning in place for the region from mid-afternoon until 8pm Thursday.

"Severe gale easterlies gusting 120km/h in exposed places, with damaging gusts of 140km/h possible overnight Wednesday and Thursday morning, especially in the north. Moderate chance of upgrading to a Red Warning," the forecaster said.

Orange rain warnings were also issued for Coromandel Peninsula, Bay of Plenty west of Kawerau, including Rotorua and the Kaimai Range, Gisborne north of Tokomaru Bay and Tasman northwest of Motueka.

A heavy rain watch was also issued for Auckland, and Great Barrier Island from 1am tomorrow into Friday.

Auckland was also subject to an orange strong wind warning from 9pm.

Overnight, Fiji's Meteorological Service upgraded a tropical low that's been hovering over Vanuatu to a Tropical Cyclone.

Cyclone Tam is a category one system moving south-south/east away from Tanna Island towards New Zealand.

Whangārei mayor Vince Cocurullo told RNZ there had been a couple of trees down and Northpower staff would be out and about to keep power on.

Far North District Council mayor Moko Tepania, speaking from Kaikohe, told RNZ it had rained all night but had eased off slightly.

Civil Defence Northland said this morning "we are starting to see some heavy rain make its way across parts of the region".

"So, as you head out this morning, please drive to the conditions, take extra care, and report any weather-related issues on the roads or in public areas to the local council."

In a post to social media, New Zealand Transport Waka Kotahi urged commuters to be wary of strong winds on the Harbour Bridge today due to strong winds.

"Please obey speed signs and maintain a safe following distance. The bridge will operate with 4 lanes in each direction today."

Vector also urged caution.

"Strong winds and heavy rain have been forecast across the next few days, and that could cause power outages as trees and branches come down over lines.

"Please remember to stay well clear of any fallen power lines or damaged electrical equipment, treating them as live, at all times. Call 111 if you do see any.

"Our crews are ready to respond as needed to restore power, as quickly and safely as they can."

Heavy rain warning - orange

Northland - 36 hours from 9am Wednesday to 9pm Thursday.

Coromandel Peninsula - 36 hours from midnight Wednesday to midday Friday.

Bay of Plenty west of Kawerau, including Rotorua and the Kaimai Range - 36 hours from midday Thursday to midnight Friday.

Gisborne north of Tokomaru Bay - 27 hours from 9pm Thursday to midnight Friday.

Tasman northwest of Motueka - 30 hours from 6pm Thursday to midnight Friday.

Strong wind warning - orange

Northland - 29 hours from 3pm Wednesday to 8pm Thursday.

Auckland and Great Barrier Island - 27 hours from 9pm Wednesday to midnight Thursday.

Heavy rain watch

Auckland and Great Barrier Island – 26 hours from 1am Thursday to 3am Friday.

Strong wind watch

Coromandel Peninsula, Waikato and Waitomo – 27 hours from midnight Wednesday to 3am Friday.

Taumarunui and Taihape - 24 hours from 6am Thursday to 6am Friday.

Taranaki about and west of Taranaki Mounga - 24 hours from 6am Thursday to 6am Friday.

Buller - 24 hours from 3am Thursday to 3am Friday.