MetService is warning of heavy rain, isolated thunderstorms and severe gales for the North Island and upper South Island today.
Severe northwest gales are expected from inland Canterbury up to Wairarapa, including Wellington.
Heavy rain from Wairarapa to Marlborough during the day is expected to ease tonight, with heavy rain predicted for Fiordland and Westland from Friday afternoon.
More severe gales are forecast to develop from Friday afternoon or evening, and gusts of around 120kmh are likely from a time in inland parts of Canterbury, eastern Marlborough, Wellington and Wairarapa.
Winds of that strength can damage trees, powerlines and unsecured structures and make driving hazardous, MetService advised.
Conditions should ease over the lower South Island overnight Friday and over the upper South Island and central New Zealand during Saturday.