Metservice meteorologist April Clark said wet weather, which swept across Hawke's Bay thanks to a lower pressure system north of Auckland, Northland and Coromandel, would linger throughout Queen's Birthday weekend.
Localised downpours and thunderstorms are possible in Auckland, with rainfall intensities of 25mm to 35mm per hour, until late morning.
MetService has advised people in Auckland's north, including Great Barrier Island, to look out for rapidly rising rivers and streams.
South Island roads are set to get slippery with snow.
Two road snowfall warnings for Canterbury's Lewis Pass and Porters Pass have been issued by MetService.
Lewis Pass can expect sleety showers that should develop into Sunday morning.
The sleet may briefly turn to snow on the summit, but the amount shouldn't be too heavy if any snow should settle, MetService said.
Porter's Pass can also expect sleety showers which should develop before dawn on Sunday.
The showers may briefly turn to snow about the summit where 1cm to 2cm may settle.
Occasional rain and cloudy periods were forecast for the rest of the weekend.
It will be a soggy start to the first Lions game in Whangarei tonight, although it's expected the rain will have eased by kickoff at 7.30pm.
Temperatures will remain steady in Auckland with a high of 16C and a low of 7C today and 15C and 8C tomorrow.
The weather will continue to ease on Tuesday and Wednesday with occasional showers.
The NZ Transport Agency urged travellers to take extra care this weekend as winter sets in.
The organisation's regional director for Auckland and Northland Stephen Town said if driving conditions were difficult, to drop driving speeds 10km below the legal limit.
"If there is a crash, the speed you're driving will determine the severity of that crash."
In the past five Queen's Birthday weekends, 172 people have been injured or killed in crashes on state highways and other roads in the Northland and Auckland area.
New Zealand police's acting national manager of road policing Inspector Gini Welch also urged drivers to be patient.
"While we cannot control other people's behaviour, we are responsible for our own actions on the road."
Last Queen's Birthday Weekend 11 people died on the road. The lowest number of deaths was zero in 2013.
The holiday road toll currently stands at one, after a pedestrian in Napier was hit by a car on Friday about 11pm.
The official holiday weekend runs until 6am on Tuesday.
