The summer-like weather is set to fade this week with rain forecast for much of the upper North Island from tomorrow.
Boaties, beachgoers and swimmers flocked outdoors this weekend as temperatures reached 20C in Auckland and Northland, and went as high as 22C in Hamilton.
MetService meteorologist Elke Louw said by midweek the mercury would sink back to the mid-teens.
Cloud coverage was due to increase for Waikato, Auckland and Northland tomorrow afternoon, turning to showers in Auckland and Northland. Northerly winds were due to freshen, bringing rain to the Waikato and Bay of Plenty in the evening, then turning to the southwest.
Showers would continue on Wednesday, when the coldest temperatures could be expected. The cold, wet weather was also due to spread to Gisborne and Hawkes Bay.
"Across the [upper North Island] it's going to get in the high-teens but for Wednesday we are looking at temperatures dropping by a few degrees but still in the early- to mid-teens.
By Thursday and Friday it is looking to clear up again," she said.
WeatherWatch predicted a cold snap that will see temperatures failing to reach double digits in Otago and Southland from this afternoon.
Today: Fine for the upper North Island
Tomorrow: Rain in Northland, Auckland, Waikato and Bay of Plenty. Temperatures dip to high-teens.
Wednesday: Rain spreads to Gisborne and Hawkes Bay. Temperatures mid- and low-teens.