Central North Island may face a battering this evening as a severe thunderstorm watch is announced, with rain predicted to reach up to 40mm per hour.
This could mean surface flash flooding and slips around low-lying areas such as rivers and narrow valleys.
Daytime heating and wind convergences were expected to produce showers around the central North Island and upper South Island during the second half of Tuesday, Meteorologist Josh Griffin said.
The warming weather meant there was a moderate risk of thunderstorms from north of Wellington to the south of Auckland.
"We have a low spinning off in the Tasman Sea, bringing cloud cover over the South Island and scattered rain.
"For the North Island, it will be convected with showers across most of the North Island and it should spin through the rest of the week."
This morning MetService issued a severe thunderstorm watch for the central North Island.
"For Taupō, eastern Taumarunui, Taihape, inland Hawke's Bay and northern parts of Whanganui, Manawatu and the Tararua District there is the potential that some of these thunderstorms become severe, bringing localised downpours with intensities of 25 to 40mm per hour.
"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."
In the South Island there was a moderate risk of afternoon and evening thunderstorms around inland areas of Nelson, Marlborough and northern Canterbury.
"These thunderstorms have the potential to bring localised heavy rain with intensities of 10 to 25mm per hour and small hail," MetService said.
Yesterday, several towns reached into the high 20s with Rotorua recording 28.4C, making it the warmest December day on record for the city.
It comes as MetService was forecasting a mixed week of weather, despite a lingering high-pressure system.
Fronts were set to move across the country mid-week, bringing wet and cloudy conditions along with humid, muggy air for the top half of the country.
"A low-pressure system moves in from the Tasman Sea on Tuesday through Thursday, producing showery conditions and possibly a period of rain for northern areas," MetService meteorologist Tui McInnes said.
"Some of these showers may be heavy with possible thunderstorms inland, particularly later in the week."
But the news wasn't all bad.
"Because the conditions are expected to be mostly showery, not everyone will see the wetter weather," McInnes said.
"Showers by nature are localised, meaning that the rainfall is not persistent and not widespread."
This meant that Kiwis could still expect some fine breaks through the week.
Whangarei: Cloudy periods, a few showers from afternoon. Sea breezes.
High 24C Low 15C
Auckland: Morning cloud then fine spells. A few showers from afternoon. Sea breezes.
High 24C Low 16C
Tauranga: A few showers, possibly heavy from afternoon. Light winds.
High 21C Low 17C
Whanganui: Fine morning, then a few showers from midday. Light winds.
High 23C Low 14C
Napier: Cloudy periods, a few evening showers. Northeast breezes.
High 20C Low 15C
Wellington: Cloudy periods. Chance evening shower. Light winds, evening northerlies.
High 21C Low 14C
Christchurch: Cloudy, and light rain at times. Northeasterlies.
High 16C Low 13C
Dunedin: Cloudy, and rain at times. Northeasterlies.
High 15C Low 12C