The combination of stormy weather and king tides could flood some low lying sections of the Auckland motorway tonight.
The severe weather is expected to hit parts of the North Island this weekend as a low moves across the country.
NZTA Auckland State Highways Manager Tommy Parker said heavy rain and winds will coincide with king tides peaking at 3.5 metres - about half a metre higher than normal - on Saturday evening and again on Sunday morning.
There was a risk that the wind and tides could cause some flooding on low lying sections of the motorway network, particularly the causeway crossing the harbour on the Northwestern Motorway.
"Weather can change dramatically, but we would advise drivers to be aware of the risk flooding and to take extra care - drop your speed by 10kph and increase your following distance," Parker said.
"High winds will have a greater impact on wave splash, particularly at high tide."
Parker said all road users needed to take care on exposed sections of the network, particularly the Auckland Harbour Bridge, during the strong winds, and to be aware of surface water because of the heavy rain.
Bursts of heavy rain are expected for northern parts of the North Island overnight tonight and through tomorrow, said the MetService.
"A low is expected to move southeast across Waikato and Bay of Plenty Saturday night and Sunday morning.
"Rain and strengthening northerlies are expected to spread over northern parts of the North Island during Saturday, with some heavy falls Saturday night and early Sunday morning."
Rain could reach warning amounts around northern and eastern parts of Northland, the Coromandel Peninsula, Bay of Plenty, northern Taranaki, Waikato, Waitomo, and Taupo.
MetService warned of possible thunderstorms during Saturday evening and early Sunday.
Northwest gales were also likely to hit exposed areas of Canterbury, Otago, Southland and Fiordland from this evening into tomorrow morning.
MetService warned the winds may reach severe gale at times.