The coldest point of the night last night for most of the upper North Island was still 20 degrees with humidity between 90 and 100 per cent.
Today will be no different WeatherWatch warned, with wet, warm air left over from Cyclone Winston 'stuck' over the upper North Island for the next couple of days.
Areas lower down the country could expect relief from humidity as a cold change swept up the South Island from today, reaching over two thirds of the country by Tuesday.
"Normally a big powerful high is oval in shape and has quite a strong look to it - but this incoming high looks like it has a puncture in the north eastern corner" said head weather analyst Philip Duncan.
"The 'puncture' I refer to is where this energetic sub-tropical air lies, and despite the incoming high this area of humidity won't budge much until the end of the week".
Mr Duncan said the peak of the humidity for many places will be today - but that downpours and moderate to high humidity may remain for northern New Zealand over the coming couple of nights, and possibly longer in Northland.
As of 10am air temperatures in Waikato, Northland and Auckland were only in the low 20s but with humidity levels around 98 and 99 per cent the 'feels like' temperature was more like 30C, especially if people were moving around.
In contrast, the lower South Island was much cooler with Dunedin on 11C and 57 per cent humidity, while Invercargill further south has just 10C.
Metservice has issued a heavy rain warning for Auckland, Waikato and parts of the Coromandel this afternoon and early evening.
It warned rainfall accumulations may reach 50 to 70mm over a 6 hour period which could cause surface flooding, making driving conditions hazardous.
The week ahead
Whangarei - The north is forecast to have more cloud, hot weather all week.
Auckland - The Queen City is in for more hot, muggy weather with temperatures in the mid-high 20s and several chances of rain.
Wellington - Mostly clear skies ahead for the capital, with temperatures forecast to be in the low-mid 20s.
Christchurch - A cooler start to the week with temperatures in the late teens, forecast to climb to 26C on Thursday and 30C on Sunday.
Dunedin - A cooler start to the week is forecast with temperatures picking up to the mid 20s as the week progresses.
How to beat the heat
Herald Facebook followers have shared their best ideas for keeping cool. Here are some of our favourites.
•"Ice water in a hottie bottle under the feet works a treat :) Or put it in the freezer with water in for 1 hour, don't forget that its in there tho!!!"
•"Wet a sarong, wring it out so just damp, place on your naked body with a fan going - the sarong dries as the night gets cooler :)"
•"I live in the tropics and have a ceiling fan, have a cool shower and wear a damp t-shirt to bed"
•"Don't forget your animals! Four legged ones!"
Keeping your bedroom cool
Dr. Alex Bartle of the Sleep Well Clinic said the optimal temperature for sleep is between 16 to 18C but getting your bedroom under 20C will suffice.
He said a cooler bedroom can be achieved by keeping the room dark during the day. Having the curtains closed and the door shut will prevent sunlight getting in and heating the room.
While air-con is ideal, a cheap fan will do the trick. Fans not only circulate and cool air, they also provide white-noise which is proven to help people sleep.
White-noise is a sound which remains constant without frequency fluctuation. The 'background noise', which can be the sound of the ocean, washing machine, or in this case, fan provides a barrier to other sounds which are more variable like a dog barking.
Humans are conditioned to be responsive to sound during sleep as a survival mechanism, but white-noise will mask other variable noises allowing us to sleep peacefully.