A red thunderstorm warning has been issued for Auckland, with MetService warning of "torrential rain".
The warning was issued for Kaipara, Auckland City, Waitakere, Franklin, Rodney, Gulf, and Albany at 2.41pm.
"These thunderstorms are expected to be accompanied by torrential rain," MetService said.
"Torrential rain can cause surface and/or flash flooding about streams, gullies and urban areas, and make driving conditions extremely hazardous."
The National Emergency Management Agency recommends people in affected areas take shelter indoors, avoid sheltering under trees, and get back to land if they're on the water.
It is advising people to move cars under cover or away from trees, secure loose objects, and clear drains and gutters.
Motorists should be prepared to stop or slow down, watch for fallen trees and powerlines, and avoid streams and drains.
A social media user from Kaukapakapa said the region was getting a "hiding" with rain "absolutely pouring and deafening cracks and rolling thunder/lightning". They also reported losing power twice.
Another user said their windows were "rattling" and their house was "shaking".
WeatherWatch.co.nz reported more than 2000 lightning strikes recorded in an hour – almost entirely over Northland as the most active band moved over the region.
A severe thunderstorm watch remains in force for Northland, Auckland, Great Barrier Island, Coromandel Peninsula, Waikato and Bay of Plenty.
Earlier, the agency warned there could potentially be surface or flash flooding, especially in low-lying areas such as streams, rivers or narrow valleys.
"Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain."
It's also set to be a muggy day, 1News weather presenter Erin Conroy told Breakfast, with some regions hitting 30C.
"We're seeing this really warm airflow just take charge, and it's drawing this moist air down from the tropics. And add in the rain and showers, it's kind of those prime frizzy-hair conditions."
Temperatures would be high in the east today, with Hastings hitting 30C and 28C in Christchurch and Ashburton.
"That is set to stick around, especially in the east for some of the weekend.
"That's 10 degrees above where we'd normally be. It's set to peak today, but that is dropping off a little bit over the weekend, but still some warm spots for sure."
How is the weather looking for election day?
1News weather presenter Erin Conroy tells Breakfast voters should get out early if they want to stay dry. (Source: Breakfast)
Conroy said the best way to avoid a wet voting experience was to "get out early".
She said the South Island was the "pick of the bunch", with rain in the west and scattered showers elsewhere – possibly turning heavy for Nelson and Marlborough.
"They could even spark up a bit of thunder and lightning there. The bottom of the south is probably the pick of the bunch for election day."
It would be a "messy day" for the North Island, Conroy said.
"If you're in the lower North, the advice is to get out early and vote. It's a bit drier there, but we've got some quite heavy rain over the top of the North Island, and that's working down through the day."
The top of the North Island might get a bit of a break, but rain could intensify through the day.
"We're looking at some pretty and some potential thunderstorms through that.
"It could be an interesting voting experience."
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