Wind gusts measuring 110km/h have been measured on the outskirts of Auckland as the city prepares for a blustery night.
People in Auckland, Northland and the Waikato are being advised to tie down loose objects as a storm packing gale-force winds of up to 120km/h is expected to lash the region from 10pm.
Drivers have already reported being pummelled by wind on motorways, with the MetService recording a gust close to 100km/h on Auckland's Harbour Bridge.
The NZTA warned drivers to take "extreme caution" crossing the bridge this evening.
A slip has also closed a section of Scenic Drive in the Waitakeres, just south of the intersection with West Coast Rd. The road is closed from the Arataki Visitor Centre.
MetService meteorologist Ravi Kandula said any gusts over 100km/h had been mainly through the Manukau Heads and out in the Hauraki Gulf but they would start to blow through the city in the evening.
Any showers so far have been short and sharp, with nowhere accumulating more than 25mm of rain.
Meteorologist Tui McInnes said the storm could be strong enough to blow objects into the air.
"You might see your trampoline has tipped itself over," he said. "Don't keep loose things around in your garden that could be picked up by the wind and rolled into a glass window."
The gales are expected to last into the early hours of tomorrow morning, with a lower possibility of high winds in Hawke's Bay.
McInnes said by 6am tomorrow most of the strong winds should be easing.
He said the rain which has hit much of the North Island this morning is the "precursor" to the bad weather on its way across the Tasman Sea.
"It's wet for most. It's pretty persistent now but the showers in behind mean it's probably not going to feel like it's getting any clearer," he said.
Electricity lines company Vector reiterated the MetService warning about tying down loose items outdoors.
"As always, we'll have crews on standby in case wind or trees bring down power lines, although our crews may be unable to attend while the wind poses a safety risk.
"If you do happen to see lines down, always treat them as live. Keep well away and call 0508 VECTOR [0508 832 867] to let us know."