The low-pressure system is expected to continue to bring showers and some clouds along the eastern and lower parts of both islands, which would influence temperatures.
South Island inland areas could even see temperatures in the negatives, MetService meteorologist Mmathapelo Makgabutlane said.
Most of the South Island woke to single-digit temperatures on Wednesday, with Christchurch, Blenheim, Queenstown, and Timaru among the coldest areas.
For the remaining days this week, Christchurch's expected low temperatures range from -4 deg C on Thursday to 1 deg C on Wednesday.
For Timaru, the low range is from -3 deg C to -1 deg C, for Blenheim -2 deg C to -1 deg C, and for Queenstown -4 deg C to 2 deg C.
A high temperature of 4 deg C on Thursday in Wanaka was about four degrees below average, MetService said.
"Still a long way off the coldest maximum of -1.1°C at that station."
In the North Island, the coldest temperatures could be in TaupĹŤ with a low of -3 deg C on Wednesday and -1 deg C from Friday to Sunday, Rotorua with a low of -1 deg C on Wednesday and 0 deg C Thursday, Saturday, and Sunday, and Hamilton with a low of -1 deg C on Thursday and 0 deg C on Wednesday, Saturday, and Sunday.
The low-pressure system was also expected to continue to cause rough sea conditions over the next day or so, Makgabutlane said.
"Combined wave heights around the eastern parts of both islands could be around four to six metres, so if you are planning on being near the coast over the next day or so do definitely take extra care around that."
Earlier on Wednesday, large swells forecast for the Cook Strait prompted Bluebridge to cancel some ferry sailings. The Interislander has also cancelled all its sailings through to Thursday morning.
The low-pressure system is expected to start moving away on Thursday and should be replaced by a high-pressure ridge.
"By the end of Friday, however, we are expecting this next weather system to start making its way, may be a bit of a showery start to the weekend down south."
