"We've got a cold front crossing over the North Island today," Holland said.
"It's got cold air behind it so we've got an unseasonably cold snap, possibly becoming frosty in sheltered inland areas in the central North Island and South Island.
The frost could be a nuisance for gardeners in inland areas, he warned.
Those in coastal areas didn't need to worry about frost killing off their summer gardens.
Christchurch was also forecast to be chilly today, with southwesterlies, showers and the possibility of snow about the hill tops of Banks Peninsulas predicted.
It would be clearer on the west coast of South Island, mostly fine in Westland with a few showers in Buller.
The maximum temperature for Greymouth and Hokitika was about 15 today, Holland said.
From tomorrow the rain would start to clear, with a few showers in the far south but generally increasing sunny spells over the whole country.
Temperatures weren't due to pick up until Monday or Tuesday and mornings might still could be frosty on Sunday and Monday for those inland on both islands, Holland said.
Temperatures around the country today
Whangarei: Showers clear early morning, then fine. Southwest. High of 19, low of 9
Auckland: Showers clear early morning, then mostly sunny. High of 17, low of 9
Hamilton: Some morning cloud, chance shower, then fine. High of 17 low of 5
Tauranga: Few early showers, then fine. Showers return at night. Southerlies. High of 19, low of 8
Taupo: Mostly fine. A few evening showers, chance heavy. High of 16, low of 3
Wellington: Cloudy periods, a few showers. Strong southerlies easing. High of 12, low of 7
Christchurch: Showers easing afternoon & fine breaks increase. High of 12, low of 5
Greymouth: Mostly fine, a few showers this morning. Dying southwest. High of 15, low of 5
Queenstown: Odd shower clearing to fine morning. Southerly dying out. High of 12, low of 0