Severe thunderstorm watches have been issued for Northland, Auckland and much of the North Island, with localised downpours of up to 40 millimetres per hour possible.
Fresh watches were issued by MetService just after 11am on Thursday and are in place for much of the North Island until 10pm.
The watches cover Northland, Auckland, Great Barrier Island, Coromandel Peninsula, Waikato, Waitomo, Taumarunui, Bay of Plenty, Rotorua, Taupō, Gisborne, Hawke’s Bay and Taihape.
MetService said a very humid and unstable northwest airstream lying over the North Island was to blame.
It is bringing a broad moderate risk of thunderstorms for much of the northern and central parts this morning until evening, meteorologist Arno Dyason said.
Dyason said localised downpours of 25 to 40mm per hour were possible.
Any thunderstorms that occur may also produce localised wind gusts of 90km per hour and hail of 10 to 20mm in diameter, he said.
This affected Great Barrier Island, the Coromandel Peninsula, Waikato, Waitomo, Taumarunui, the Bay of Plenty, Rotorua, Taupō, Gisborne, Hawke’s Bay and Taihape.
“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.
“Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain.”
A severe thunderstorm warning was issued for the Hauraki Gulf and Thames Coromandel area at 1.45pm.
This was because a MetService weather radar had detected severe thunderstorms near Waiheke Island.
They were expected to hit Manaia and near Whitianga and Coroglen by 2.30pm.
The thunderstorms were expected to be accompanied by torrential rain and frequent lightning, MetService said.
Dyason said there is also a moderate risk of severe thunderstorms for western areas from Northland and Auckland down to Taumarunui on Thursday morning and afternoon.
This watch is in place until 5pm, with localised downpours of 25 to 40mm possible.
Other weather watches and warnings
MetService has also said there is a heavy rain warning in place for the ranges of Westland, south of Otira, and Fiordland on Friday.
For the ranges, this warning is in place from 4am until 11pm, with 100 to 130mm of rain expected.
For Fiordland, this is in place from 1am to 10pm, with 60 to 90mm of rain expected.
There is also a heavy rain watch in place for the ranges of eastern Bay of Plenty and Gisborne on Thursday.
This is the same for the Canterbury Headwaters from Arthur’s Pass southwards and the Otago headwaters.
MetService has also issued a strong wind watch for the Canterbury High Country on Friday, the Southern Lakes, and Fiordland and Southland west of Athol to Riverton.
Thursday’s thunderstorm watches are not the first to hit the country this week.
A severe thunderstorm watch was in place on Monday for parts of Auckland and Northland.
On Wednesday, the upper North Island was at risk of severe thunderstorms , with downpours and hail, through Wednesday afternoon and into the night.