A MetService spokesman said a west to southwest flow would cover New Zealand tomorrow, possibly bringing warning amounts of rain in Fiordland and severe westerly gales in the south of Southland, including Stewart Island and Clutha.
A strong wind watch has been issued for coastal Southland and Stewart Island, running from 11pm Monday until 8am Tuesday.
"On Wednesday, a large trough over the Tasman Sea with an embedded rain band will move north over the South Island, followed by a change to strong cold southerlies."
He said it was likely there could be warning amounts of rain for Fiordland and Westland and it was possible northwest winds could rise to severe gales for a time about high-country areas of Canterbury, inland Otago and inland Southland.
"In eastern and southern areas of the South Island, a period of rain is expected from Wednesday into Thursday with snow lowering to about 400m.
"The duration and intensity of the rain may not be long or heavy enough to approach warning thresholds, however snow could significantly affect some roads and passes in the South Island."
On Thursday, the trough and associated rain was expected to move on to the North Island, but significant uncertainty remained regarding the distribution of rain and strongest winds on Thursday and Friday, he said.
"MetService will continue to monitor the situation."
