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"Drive to the conditiions. If it's windy and you're in a high-sided vehicle be very careful and the same for motorcycles in those exposed areas."
Traffic was starting to build up on the Southern Motorway with queues around Greenlane and Market Rd.
A crash is blocking the right lane southbound on the Southwestern Motorway before the Massey Road offramp. NZTA urged motorists to pass with care.
Some passengers have been stranded at Auckland Airport after their flight to Queenstown was cancelled.
Earlier, motorists crossing the harbour bridge were warned to go slow as loud hail hammered down.
Video of hail pelting down on a car as it crosses the Harbour Bridge has been released by 1News.
Other Aucklanders posted to social media showing a smattering of hail in the backyard before it melted on the ground.
Just after 5.30am a motorist had a lucky escape when a large tree crushed a car on State Highway 22 near Pukekawa south of Auckland. It's the second time in two months a moving vehicle had been crushed by the cluster of trees, and Mercer deputy fire chief Richard Logan said he was disappointed the trees were not removed after a woman's car was crushed in May.
Around 11m of rain has fallen around the city today with a further 3mm forecast.
Earlier in the day traffic lights went out at some Ellerslie intersections. They have since been restored.
Tomorrow will have a wet start with showers and possibly heavy downpours until midday. The wet weather will then clear in the afternoon and into Sunday.
Marsters said the weather would start to ease from tomorrow afternoon. The northwesterly would swap to a southwesterly which would bring cooler temperatures.
"It's not until Sunday you see some sunshine."