Muggy nights are on the cards over the next few days as a sub-tropical airflow moves over parts of the country this week.
That may also bring some heavy rain and thunderstorms tomorrow and Friday, as moisture is brought southward from the tropics, weather experts say.
MetService says humid conditions can be expected as a result; with some reprieve - albeit colder temperatures - on the forecast towards the weekend.
In Auckland, temperatures are set to be in the low to mid-teens this week.
MetService meteorologist Andy Best said the moist air coming in from the tropics would see parts of the North Island - from Waikato to the Kapiti Coast - experiencing muggy nights through to tomorrow night.
Conditions are due to become more unsettled towards the end of the week as a frontal system goes over the North Island, he said.
"Warming up too in parts of Gisborne, Hawke's Bay and Wairarapa with forecast maximum temperatures in the mid-twenties."
Aucklanders are experiencing a high of 21C today and an overnight low of 15C.
A WeatherWatch spokesman said: "The warmer than usual run of weather is being caused by a sub-tropical or northerly flow which is spreading down over the North Island and some parts of the South Island."
Inland parts of the South Island are showing over 8 degrees above normal temperatures by day.
Although some coastal areas are reporting a cooler sea breeze, many places inland are warmer than usual as a result.
"The mild run of weather continues on this week even as a low in the Tasman Sea moves through then falls apart," he said.
Temperatures will see a marked drop later in the week, with Invercargill set to see a shift from a high of 21C on Saturday to 11C the next day.
Alexandra will from a warm high of 22C on Friday to 14C on Sunday.
"For many, the cooler Sunday and Monday change will only reset temperatures back to normal for this time of year."