A strong wind watch has also been issued for the Canterbury High Country from 10am, with north-westerlies expected to approach severe gale force in exposed places.
The wet weather is expected to reach Wellington, the Kāpiti Coast and Taranaki late tomorrow before spreading north overnight into Friday.
MetService has issued a heavy rain watch for the Tararua Range from midnight tomorrow until midday Friday.
Strong wind watches are also in place for Wellington tomorrow night, and coastal Southland, southern Fiordland and coastal Otago on Friday.
Auckland is forecast to remain largely dry through tomorrow before rain arrives overnight.
“On the plus side, with a bit more cloud around and some stronger winds and some slightly milder air, temperatures won’t be a concern tomorrow night,” Law said.
However, the reprieve would be short-lived. “We’ve not seen the back of those cold temperatures as we head in towards the weekend.”
As the front clears, a surge of cold Southern Ocean air is forecast to push north sending the country “back into cold frosty conditions” on Friday.
Law said Friday was shaping as “a pretty nasty feeling day” for the far south, with Southland, Clutha and the Dunedin coast hardest hit by gusty southerlies and freezing downpours.
The cold blast is expected to reach Wellington on Saturday morning, when strong southerlies are forecast to make an early start feel “pretty raw”, while Wellington and Christchurch struggle to highs of 8C or 9C.