Heavy rain predicted to hit the South Island tomorrow has forced the closure of Milford Rd.
Northwest gales and rain are expected to hit areas of the south and central New Zealand, ahead of a front passing over the Tasman Sea, MetService said.
Westland and Fiordland will have a period of significant heavy rain tomorrow, which could affect the Otago and Canterbury lakes and rivers.
"Heavy rain is also likely to reach warning levels in parts of Southland," MetService said in a statement.
"The heaviest rain is expected in Westland where 350mm could accumulate in the ranges south of Otira during a 24 hour period."
MetService said this kind of downpour would see water levels in rivers and streams rise quickly, and could lead to slips and flooding.
Milford Rd will close tonight and remain closed all day tomorrow as a "precautionary measure", the NZ Transport Agency said today.
The road has been closed each night between the Homer Tunnel and Murrell's Bridge from 7pm to 7am since the end of November because of concerns over rockfall risk in the area.
NZTA's Southland State Highway operations manager Peter Robinson said the closure was a precautionary.
"The heavy rain that has been forecast is for tomorrow only; we expect the road to open again on Thursday and to remain open for the remainder of the week, with only showers forecast."
He said the opening time on Thursday would depend on weather conditions in the morning and motorists are advised to check the NZTA website.
The nightly closures of the Milford road are expected to continue to the end of January as NZTA works to manage rock fall risks in the area.
The NZTA said it had been working closely with local tourist operators to minimise the impact of the closures during the peak tourist season.
Gale force winds are expected to reach a severe strength in Otago, Canterbury, Marlborough, Wellington and Wairarapa.
Wellington and inland Canterbury should see the strongest winds, with gusts up to 140kmh.