Weather: Ferries cancelled, motorists warned as deluge bears down

Auckland ferries have been cancelled and Otago motorists warned to watch out for "summer ice" as bad weather bears down on New Zealand.

MetService has issued a warning for heavy rain on Wednesday as storm clouds loom.

"Rain is coming!" it warns.

"An active front moves slowly across New Zealand from today (Wednesday) through to Friday, bringing a period of rain to much of the north and west of the country.

"Heavy rain warnings are in force for southern Westland, Nelson, northern Marlborough, Northland, Auckland, and northern parts of Taranaki."

Meanwhile, Auckland Transport is warning commuters that Gulf Harbour ferry services have been replaced by buses due to weather conditions.

And the New Zealand Transport Agency is warning motorists to take care, with the danger that rain in Otago could lead to "summer ice" conditions.

"When it rains, the road surface becomes greasy, making it very slippery - the greatest risk to drivers being shortly after the rain starts," it advises.

"The term 'summer ice' is used to describe these conditions that are similar to the black ice that you get in winter.

"Even a little rain after several days of dry weather can trigger these conditions, creating a potential danger for unsuspecting drivers."

Fortunately, other parts of the country will be spared the rain.

"Not everywhere will see large amounts though. In general eastern areas will see much lighter rain, and it won't arrive in Hawke's Bay/Gisborne until tomorrow," MetService says.