A cold front, moving northeast, is expected to move on to the South Island during Friday, bringing rain to the west and strong west-to-northwest winds to the south and east of Otago and Southland.
A MetService spokesman said it was possible a heavy rainfall warning would be required in Fiordland, and a wind warning might be issued for Fiordland and Stewart Island where there could be severe gale west-to-northwest winds.
About inland areas of mainland Southland, Otago and Canterbury, there was also a possibility that northwest winds would reach warning strength, he said.
The front was expected to continue moving northeast over the South Island during Saturday and weaken.
"There is a chance a low will develop on the front, east of the South Island.
"There is likely to be rain for much of the South Island and southern North Island.
"Strong northwest winds ahead of the front should ease in the afternoon.
"Snow is possible about the southern and central South Island, but the level it falls to is uncertain at this stage."
He said it was possible that snowfalls above 700m in Otago and South Canterbury, would be heavy enough to require a warning.
He said it was also likely a rainfall warning would be needed for Fiordland and the ranges of the Westland District on Saturday.
A weak ridge of high pressure was expected to form over New Zealand during Sunday, he said.
