MetService is warning that heavy wind and rain could strike much of the South Island today, and fog is causing flight and ferry disruptions in Auckland.

Northwest gales were forecast for the lower South Island including Dunedin and North Otago from early Friday morning to Friday night.

The ranges of Marlborough and Wellington could expect strong winds from Friday night through to Saturday 3pm and strong winds for Wairarapa south of Carterton were expected early Saturday morning to early Sunday morning.

The gales will affect the Canterbury High Country later in the morning, and Christchurch and the Canterbury Plains from afternoon.

Heavy rain was expected in Fiordland from late-morning, in Westland and the Southern Lakes from Friday afternoon and in the Canterbury High Country Friday night.

Auckland was covered in mist for a second consecutive day, bringing flight cancellations and ferry delays for commuters.

This morning Air New Zealand said 20 regional flights had been cancelled so far due to poor visibility for the aircraft.

The West Harbour, Hobsonville, and Beachaven ferry services had been delayed by 30 minutes and Pine Harbour ferries were also expecting delays.

The fog was expected to lift mid-morning.