KEY POINTS:
The humidity level in Auckland last night peaked at 100 per cent according to Newstalk ZB's weather analyst.
Philip Duncan said overnight temperatures in the city hardly fell below 23 degrees.
He estimated that, combined with the humidity, it felt more like 32 degrees.
Mr Duncan said when humidity reaches 100 per cent the air is completely saturated and sweat cannot evaporate from skin.
At 10am this morning, MetService said the humidity level in Auckland was still 90 per cent.
The muggy conditions, which were also felt in Whangarei, have been caused by a low north of the country pulling air straight from the sub-tropics.
It is a different story in the South Island, where single digit temperatures have been recorded thanks to a cold southerly change.
MetService spokesman Bob McDavitt said that last Sunday could have been the hottest day of the year.
"The air is still very warm and, coupled with high humidity, is bringing muggy conditions and keeping overnight temperatures up with many of the coastal parts of the North Island recording an overnight low of 20 [degrees] or more last night," Mr McDavitt said.
He said the hot air temperatures could bring thunderstorms to mountainous areas in the North Island as well as Nelson and Marlborough in the south.
Mr McDavitt said the rain should disappear tomorrow but was likely to return to the central and north North Island on Thursday.
He said a cold southwesterly change could hit the country on Friday and Saturday, bringing snow to the Fiordlands and single digit temperatures to Southland.
- NEWSTALK ZB, NZHERALD STAFF
