Meteorologist Melissa Oosterwijk said conditions will be less humid in the coming days as there will be less moisture in the air.
The present high pressure system often led to light winds, particularly in the North Island and along western areas, which resulted in not a lot of air movement - especially at night.
"That means all of the moisture that's hanging around, it doesn't go anywhere.
"We only got down to about 13C [on Saturday night] - which is reasonably warm, particularly as we're just getting used to warm temperatures again after all of winter."
Temperatures in parts of the North Island will stay around the late teens to early 20s next week. Aucklanders can expect a high of 20C tonight and an overnight low of 13C.
Hamilton has a high of 20C today also, 21C in Whāngārei, 19C in Palmerston North, 18C in Wellington and the same for those in Christchurch, Dunedin and Queenstown.