Duncan said these temperatures were over 8C warmer than the average temperatures in those areas.
Metservice meteorologist Philippa Murdoch said the ridge of high pressure would hang around the North Island for the next few days.
The North Island experienced a fine, warm autumn day. Auckland hit 23C, and Tauranga at 25C, she said.
MetService meteorologist Karl Loots said although it was warm for April, it was not unseasonable weather.
"This time of year we generally get stronger westerly flows, so every now and again can see temperatures in the high 20s."
As a weak cold front moves through the North Island this morning and afternoon there will be a few showers from Manawatu north. These will become increasingly isolated as the front reaches Auckland.
🌩A NIGHT OF RUMBLES FOR THE WEST COAST🌩
No it's not because those in the West Coast didn't have enough for dinner. An...
Posted by MetService New Zealand on Monday, 2 April 2018
In the South Island a stronger front is forecast to bring rain to Westland, Fiordland and Southland.
A weather watch is out for gale-force winds in Fiordland and Southland to 3pm today.
A ridge of high pressure will move over the central and northern parts of the country on Thursday and Friday, bringing settled weather but a few scattered showers.
Tomorrow night another front will move on the lower South Island, bringing another bout of rain to Fiordland, Westland and Southland.
On Friday morning the front will slowly track up the South Island, bringing rain to Otago and Westland in the afternoon.
Murdoch said as the front moved up the South Island it would weaken by the time it made it to the North Island.
The weekend weather is looking fairly unsettled at this stage, as several weak southwesterly fronts move over the country.
"There is no severe weather at this stage though," Loots said.
Tropical Cyclone Josie, which brought devastating floods to parts of Fiji on Sunday, has been downgraded to an ex-tropical cyclone.
"It is tracking south to southeast, and poses no threat to New Zealand," Loots said.
Sitting offshore from Queensland is Tropical Cyclone Iris, which has been upgraded to a Category 2 cyclone.
Australia's Bureau of Meteorology forecasts it to stay Category 2 for the next 36 hours and track parallel to the Queensland coast, before weakening.
It may make landfall on Australia's east coast later in the week, but will likely be a low at that stage.
Into next week, WeatherWatch NZ says a cold southerly on Sunday into Monday and Tuesday next week will see snow falling on the mountains in both islands.
Parts of the lower South Island will also see single digit daytime temperatures.
However, the cold won't last too long with more high pressure systems coming in behind it.
Tomorrow's weather
Whangarei Morning cloud then fine. Light winds. 23C high, 15C overnight.
Auckland Morning cloud then fine. Southwest breezes. 23C high, 13C overnight.
Hamilton Morning cloud then fine. Southwest breezes. 24C high, 10C overnight.
Tauranga Fine and partly cloudy. 25C high, 14C overnight.
New Plymouth Fine then cloudy in afternoon. 22C high, 11C overnight.
Napier Fine then cloudy periods in afternoon. 23C high, 12C overnight.
Wellington Fine. 20C high, 14C overnight.
Nelson Fine. 21C high, 10C overnight.
Christchurch Fine apart from morning cloud. 18C high, 7C overnight.
Dunedin FIne. 20C high, 12C overnight.
