"There is a big front coming in from the Tasman on Monday afternoon which will mainly affect the western parts of the east coast," Wilkinson said.
"It will mean heavy rain in some parts of the central and lower North Island."
But despite the changeable outlook, it will be warm up north from tomorrow.
"On Monday, temperatures could get up to 23 degrees in Northland and the east coast will also be warm," Wilkinson said.
"In the South Island, southerly winds will come in behind another low from the Tasman which will mean some more cold weather travelling up the country."
Weather in Auckland is expected to be patchy today, which should brighten up as the week wears on.
"There will be cloud around on Monday morning ad a few showers," Wilkinson said. "But I expect this will clear up a good bit during the day and the sun will break through at times.
"I expect Auckland will see temperatures of about 17-18 degrees over the next few days, while it will be wet in the west of the country but drier in the east."