While conditions such as those on Saturday - when the temperature topped 25C in Auckland and didn't fall below 20C during the night - were unlikely to be repeated, there was a chance humidity levels could rise again.
"Humidity will drop over the next couple of days with the southerlies, but easterly breezes from Tuesday could lift the moisture levels again through the week," she said.
On Sunday morning, humidity reached 97 per cent in Auckland - the highest for the week.
The hottest temperature was recorded on Friday, with 28C, with a muggy 94 per cent humidity.
On Wednesday, humidity topped 88 per cent, and did not fall below 69 per cent.
According to MetService records, the sticky conditions are generally worst in the morning.
Climate scientist Dr Jim Salinger said the muggy conditions were a combination of high temperatures and airflows from the east and northeast of New Zealand.
"It's been the warmest spell of summer."
The week ahead
Auckland: Fine weather with light winds, and cloudy periods. Freshening southwesterlies from Friday. Highs of 23C, rising to 26C by Friday. Overnight lows 15C.
Hamilton: Sunny conditions, temperatures in high 20s.
Wellington: Highs of 22C with fine conditions.