The MetService is warning up to 25mm of rain an hour, or even small hail, could fall in Northland, Auckland and eastern Waikato. The western Bay of Plenty may get 100m to 140mm, the MetService says.
This amount of rain will cause rivers and streams to rise and may lead to surface flooding and slips, so the MetService has issued a severe weather warning for Taupo, Bay of Plenty and parts of Waikato.
Despite the wet, temperatures will be summery around the country, ranging from the high teens to the mid 20s.
The rain should ease to showers over Northland and Auckland this afternoon, but there's a moderate risk of early evening thunderstorms from Northland to Taranaki.
Cricket fans will be praying the thunderstorms stay away for the Black Caps match against the Proteas at Eden Park tonight. But there's more bad news for fans, as Hamilton, which will host a game tomorrow, will get a showery weekend too.
The trough will move further south as the day continues, bringing heavy rain to Taranaki, Wairarapa and eastern Marlborough.
Although the rest of the country should escape the thunder and lightning, the MetService is forecasting rain and showers for almost the entire country.
Invercargill will be the exception, with sunshine on the cards for the southern city.
The capital will get a cloudy day interspersed with patchy rain.
It will be cloudy and drizzly in Christchurch, but residents there might hope for more rain to dampen the large blazes raging in the Port Hills.
The Garden City will also get light northeasterly winds this morning, which will pick up as the day goes on, reaching an average speed of 30km/h mid-afternoon - hopefully not high enough to fan the flames.
Today's forecasts
Whangarei: Heavy rain, possible thunderstorms and light winds, high of 26C
Auckland: Heavy rain, possible thunderstorms easing tonight, northerlies, 24C high
Hamilton: Heavy rain, possible thunderstorms and a northeasterly, 24C high
Tauranga: Heavy rain, possible thunderstorms, northeasterlies. high of 23C
Wellington: Cloudy, rainy periods, southeasterlies, 19C high
Christchurch: Cloudy, occasional drizzle, northeasterly, high of 21C
Dunedin: Cloudy periods, northeasterlies picking up, 19C high
