Temperatures should remain pretty high today, with Auckland set to reach 26C, before the rain moves in later this evening.
Most North Island holiday destinations in the north and east will see rain in the coming days, developing by this afternoon or evening and continuing through to Wednesday and Thursday in some places.
Hawke's Bay will see the best of the weather today, with "only a little bit of rain", and Wednesday is set to be fine as well. Showers will arrive on Thursday and Friday, along with a cooler, southerly change.
Temperatures in the North Island will be around the low 20s or high teens.
In the South Island, cloud and rain is forecast today, particularly over the high country and ranges, and continuing into Wednesday, but turning fine by the end of the week.
The South Island will see the lowest temperatures this week, with the mercury set to drop to the mid-teens in some places.
"Even down to maximum temperatures of 14 or 13C the further south you go, so Invercargill, Wanaka and Alexandra, those places will be not as warm," Mr Oakley said.
Friday and Saturday will be the best days of the week, Mr Oakley said.
"We've got a nice ridge coming along later in the week so most of the places are looking good for Friday and Saturday."
However, Southland will continue to see showery spells into the weekend.
The unsettled weather will bring more gloom to some holiday makers who were forced to escape heavy rain, causing flooding in some parts of the lower North Island over the weekend.
Campers at Morrison's Bush campsite in Wairarapa had to scramble to safety when the Ruamahanga River rose rapidly on Sunday night.
A number of children had to be rescued by tractor after heavy downpours flooded the site, forcing some campers to abandon their tents and caravans.
