In Auckland sandbags and weights on temporary road cones have been placed along the harbour bridge, which still has lane closures after an accident.
The Transport Authority says it will reduce speeds, close more lanes "or even close the bridge if necessary".
"Safety is our absolute priority," says General Manager Transport Services Brett Gliddon.
"Motorists are urged to keep to the posted speed limit when crossing the bridge, avoid changing lanes and do not be distracted.
"We have tow trucks positioned on the bridge approaches to respond quickly to crashes and breakdowns but any vehicle stopping on the bridge will cause huge disruption that can quickly spread across the entire network."
Heavy rain warnings are in place for Westland about and south of Otirā, where people are being told to expect between 100mm to 130mm of rainfall to accumulate near the ranges and 70mm to 90mm near the coast. There is also the possibility of thunderstorms.
Locals are being warned that the heavy rain may cause streams and rivers to rise rapidly and that surface flooding and slips could happen as a result.
"Driving conditions may be hazardous," an alert said.
Strong wind warnings have been issued in the Wairarapa - not including the Tararua District, Wellington - where northwest gales are forecast to reach up to 130km/h.
WeatherWatch said a weather bomb is likely to form this weekend over the Southern Ocean, as air pressure plummets from around 980hPa on Saturday to 930hPa on Monday.
MetService has released a graph detailing exactly how bad the weather is forecast to be - with the average forecast models for Sunday looking to be one of the worst storms since at least 2014.
The weekend's weather bomb falls just above a storm in November 2018, when roads were closed on the West Coast due to flooding.
It falls just under another huge weather event in May 2014, when 4500 homes were left without power and there was massive amounts of snow in Queenstown.
Winds should be early on Sunday morning, MetService said.
Canterbury High Country is also on alert for a strong-wind warning and gusts are expected to get up to the 120km/h mark.
Meanwhile, heavy rain watches are in place for the areas including the ranges of eastern Bay of Plenty, Mt Taranaki, Nelson about and west of Tākaka, Buller, Westland north of Otirā, Tararua Range, Richmond Range including the Rai Valley and Fiordland.
People in Clutha, Central Otago south of Alexandra, Southland, Fiordland and Stewart Island are all being told to stay up-to-date with the weather conditions as there is currently a heavy snow watch in place.
While a strong wind watch has been issued for parts of the South Island including Christchurch, Central Otago, Southern Lakes, Fiordland, Southland and Stewart Island, North Taranaki across to East Cape and northwards, Hawke's Bay south of Hastings and Tararua District and Marlborough.
