The South Island and lower North Island should brace itself for a chilly snap come Waitangi Day, while the upper parts of the North Island will continue to bask in hot, hot weather.
Temperatures in Dunedin and Christchurch will plummet on Wednesday to 15C and 17c respectively - a hefty drop from the mid-20Cs and 30C temperatures on Monday and Tuesday.
Wellington, Napier and the Wairarapa would also wake up to cooler temperatures on Waitangi Day.
Niwa meteorologist Ben Noll said there was a big change coming and it would start to feel like autumn in the South Island for a few days before the warmer temperatures returned at the weekend.
"They are actually really chilly temperatures for Waitangi Day."
Noll said there was a wind shift and it would start blowing from the south it bought up colder air from the Southern Ocean.
"It happens especially as we start to get late into the summer season, you can start to see some of those cold fronts tracking up the South Island."
People in lower parts of the North Island might also be reaching for their jumpers on Wednesday as the temperature dropped from low 20s to 17C.
"The folks hanging onto the warmth will be at the tippy top of the country from about Hamilton northwards."
Whangarei was expected to reach 27C, Auckland 26C and Hamilton 25C.
Waitangi Day Weather
Whangarei - 27C
Auckland - 26C
Hamilton - 25C
Tauranga - 25C
Wellington - 17C
Christchurch - 17C
Dunedin - 16C