Taranaki and the eastern Bay of Plenty have a risk of heavy rain when that precipitation sets in.
It's a bit of a "tale of two stories" because as that front moves north the South Island starts to clear again, he said.
A very weak front was expected to follow and by Tuesday the weather could be heading towards a more settled trend again, he said.
According to WeatherWatch the "enormous" high pressure system today is perfectly centred across the country and stretches from Fiji to eastern Australia and all the way down to near Antarctica.
WeatherWatch further predicts a couple of cold nights ahead but warmer than average afternoons for many places inland both today and tomorrow.
Today's weather forecast
Whangarei:
Partly cloudy, chance shower. Southeasterlies. High 20C, Low 14C.
Auckland:
Fine. Easterly breezes. 20C, 10C.
Tauranga:
Fine. Light winds. 20C, 9C.
Hamilton:
A fine day. Southeasterly breezes, dying out in the afternoon. 20C, 5C.
New Plymouth:
A fine day. Southeasterly breezes dying out. 18C, 8C.
Napier:
Cloudy periods. Southerlies dying out. 18C, 8C.
Wellington:
Areas of morning cloud, then fine. Southerly breezes, dying out this evening. 16C, 8C.
Nelson:
Fine with light winds. 17C, 8C.
Christchurch:
Fine, but early frosts, and some morning and evening cloud. Northeast developing afternoon. 15C, 8C.
Dunedin:
Fine, morning and evening cloud. Northeast breezes developing afternoon. 16C, 9C.