A dangerous combination of strong winds and sodden ground could cause weakened trees to fall and damage electricity networks, Vector warns.
"Trees coming into contact with lines and cars colliding with power poles in the wet, are both possibilities when the worst of the weather reaches Auckland," chief network officers Andre Botha said.
The Auckland region and parts of the Coromandel Peninsula will be hit with the brunt of the wild weather, says MetService meteorologist Ravi Kandula.
Earlier, MetService issued a weather watch as a rain band and northeasterly winds made their way over the city during rush hour.
Kandula said a possibility of a tornado "certainly exists".
"As the front approaches you get gusts of 30-35 knots (55-64km/h) and that's the watch that's in place," he said earlier today.
Safety is a concern for Vector and the turbulent weather can make conditions difficult, but if residents spot any issues they should contact the relevant personnel.
"During a power outage, please remember that the safety of the public and Vector's contracting field staff is of primary importance at all times.
"Keep an eye on seemingly-weakened trees that could endanger the public or threaten to collapse on electricity infrastructure, and alert the relevant authorities.
"And most importantly, please, always treat downed lines as live and stay well clear," Botha said.
The wider Auckland region - particularly parts in the northeast - is expected to be worst hit by the weather system.
"Starting at 8 to 9pm there's a thunderstorm risk as [the front] moves down - we're expecting that risk to be confined largely northeast of the city.
"The risk of the city is lower than it is for the Hauraki Gulf," Kandula said.
Tomorrow a low and associated fronts would move slowly east over the country, bringing rain to areas and strong winds in the upper North Island.
The majority of rainfall is expected to fall tonight before easing back to showers and possible thunderstorms tomorrow.
Metservice has issued a wind warning starting at 4pm tomorrow for Auckland, Bay of Plenty, the Coromandel Peninsula and Waikato.
