MetService meteorologist Dan Corrigan says rain could exceed 25 millimetres an hour, causing flash flooding, rising rivers and slips. Photo: Unsplash / Daoudi Aissa
Thunderstorms are forecast for much of the upper North Island this evening.
Torrential rain has been reported across Auckland, with State Highway 1 southbound near the Mount Wellington off-ramp blocked due to flooding.
Police are warning people to reduce their speed while driving around the city.
The sudden change in weather also prompted Auckland Airport to cancel or delay several domestic flights.
MetService severe thunderstorm warnings for Auckland City, Waitakere, Rodney, Kaipara, Far North and Whangārei have now been lifted, however fresh ones have been issued for Waikato, Hauraki, Franklin, Matamata Piako, Hamilton City and Waipa.
The expected torrential rain could cause flash flooding about streams, gullies and urban areas and could make driving conditions extremely hazardous, the warnings said.
MetService said conditions remained favourable for thunderstorms elsewhere in the upper North Island and a severe thunderstorm watch would remain in force until 9pm for Northland, Auckland, Waikato, Waitomo, Taumarunui, Bay of Plenty, Rotorua and Taupō.
MetService meteorologist Dan Corrigan said rain could exceed 25 millimetres an hour, causing flash flooding, rising rivers and slips.
"That doesn't mean there's going to be thunderstorms everywhere all of that time, but if you're in the thunderstorm watch area, there's a risk that a thunderstorm could affect your location and it could bring a downpour of very, very heavy rain."
Temperatures in the south set to soar
High temperatures are predicted for many parts of the country this week, particularly the lower South Island.
The Hutt Valley is set to reach 28 degrees today, and Te Kuiti is going for a high of 29.
Corrigan said Wānaka was headed towards a 30-degree day on Wednesday.
"An average December day in Wānaka is 22 degrees and really the whole lower east corner of the South Island is looking at some well above average temperatures in the high 20s, low 30s."
Temperatures in Dunedin, Central Otago and Southland would spike from Wednesday, and Christchurch looked likely to reach 30 degrees on Thursday, he said.