Whangarei is also expecting a high of 21C tomorrow with wet and windy conditions.
MetService said the wet weather is also likely to hit much of the rest of the country with heavy rain warnings also likely to be issued for other areas of the North Island, as well as the top of the South Island.
It has forecast Hamilton to reach 21C tomorrow with a few showers, while Tauranga could expect 20C and heavy evening falls, while Wellington is tipped to reach 22C with morning drizzle and afternoon sunshine.
Drizzling rain is also forecast to hit the South Island tomorrow with Christchurch and Dunedin expecting a top of 17C, while Invercargill is tipped to reach 21C and Queenstown a high of 22C.
WeatherWatch said the rainy conditions were normal for the start of summer.
"December is set to start with tropical northerlies bringing moisture down over New Zealand with extra tropical heat," the forecaster said.
"When [this is] combined with our local daytime heating inland, it's the perfect recipe for big cloud build-ups, downpours and thunderstorms in the afternoon or evenings."
"This is normal weather for this time of the year as true summer starts to move in (usually kicking in properly by January)."
