After a mild morning, much of the country will get showers today - with severe thunderstorms likely to pop up in some areas this afternoon.
"Auckland may even get some hail in the afternoon," weather presenter Renee Wright said on TVNZ 1's Breakfast today.
There were thousands of lightning strikes across the North Island yesterday afternoon, MetService New Zealand said in an update posted on the agency's Facebook page.
"The thunderstorm watch and outlook charts indicate a significant risk of severe thunderstorms...Friday, with the risk spreading across northern South Island," MetService said.
The weather service attributes the storm probability to "the combination of another warm humid day and light winds".
Areas currently under severe thunderstorm watch through the evening include Northland, Auckland, the Coromandel Peninsula, Waikato, Waitomo, Taumarunui, Bay of Plenty, Rotorua, Taupo, Gisborne, Hawkes Bay, Taranaki, Taihape, Wanganui, Manawatu, Tararua, Kapiti-Horowhenua, Wairarapa, Marlborough, Nelson, Buller and Westland.
"These thunderstorms are expected to produce localised downpours of 25-40 mm/h (or more), hail 20mm diameter (or larger), and maybe wind gusts of 60-80km/h," MetService reports.
"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."
Unfortunately, the showers are expected to stick around through the weekend thanks to a "a few, almost stationary features".
"All the ingredients are in place for some significant afternoon thunderstorms over parts of both islands for the next few days," said meteorologist Rob Kerr.
"With northerlies pushing warmer, moisture laden air over the country close to the surface, and a cold pool in the upper atmosphere causing enough instability for severe thunderstorms to develop."