Heavy rain is forecast for parts of Fiordland and Westland.
MetService says a front is forecast to move onto Fiordland overnight and head north to lie over southern Westland by midnight on Saturday.
Heavy rain is forecast for Fiordland north of Doubtful Sound on Friday night and Saturday morning.
The rain should reach the ranges of Westland as far north as Otira from about dawn on Saturday.
Trampers are advised to stay vigilant, as waterways could rise quickly.