Western and southern parts of the South Island should brace for heavy rain this weekend while sunny and calm days are expected in the North Island.
MetService is predicting central parts of Westland could see between 250-350mm of rain in the next few days.
The rain is also expected to spill over into Canterbury.
A spokesperson said an active front is forecast to move slowly north across the South Island today and during the weekend, bringing heavy rain to some areas. The front may stall for a time about central or northern Westland.
They said there may be "significant impacts" in Westland as rainfall amounts in some of the townships may be unusually heavy.
"People are advised to stay up to date with the latest warnings and watches in case any changes are made, or further areas are added."
Heavy rain warnings are in place for Westland and Fiordland. Heavy rain watches are in place for Buller, the headwaters of the Canterbury Rivers and Lakes and Southland.
And the warm sunny weather felt by many in the south recently will disappear with temperatures expected to drop.
According to MetService, Christchurch is expected to reach 16C on Saturday, a sharp contrast to the 26C recorded on Friday.
In contrast, the top half of the country is expected to stay dry and settled over the weekend.
Temperatures in Auckland are expected to reach higher than 20C most days.
But more showers are due to arrive across the country on Tuesday.