The MetService said several lines of thunder showers were expected to cross the top half of the North Island today and they could include tornadoes.
"Unlike Tuesday, we can already identify tornado potential in these lines of showers," said MetService chief forecaster Peter Kreft.
"We must emphasise that right now we are not able to be more specific about the likelihood or timing of any tornado at this early stage," he said.
Mr Kreft said if tornadoes or severe thunderstorms looked increasingly likely today the MetService would issue a severe thunderstorm warning.
He said in New Zealand tornadoes were rare. They mostly lasted only a few minutes and affected very small areas.
"So on Friday they could easily occur over farmland, forest or the sea without anyone noticing them.
It's very important you know what to do to keep yourself safe."
He said the Ministry of Civil Defence and Emergency Management advice was for people who saw a tornado nearby or felt threatened by the weather, to take shelter immediately. If the threat was further away, help alert others.
People inside a building should move to the lowest floor and to an interior room (without windows or exterior door). Get under sturdy furniture or a door frame.
Outside move away from trees, lie down flat in a gully, ditch or low spot on the ground to avoid flying debris. Protect your head with your arms.
In a car, do not try to outrun the tornado. Get out and away from the car and lie down flat. Do not lie under your car.
Meanwhile, more than 200 properties have been inspected by Auckland Council building inspectors after Tuesday's tornado swept over Albany on the North Shore, down to Glenfield and across the harbour to Pt Chevalier.
Civil Defence said it was working with organisations and agencies to support the people affected by the tornado.
The council said it was assessing affected areas and making sure debris was removed as quickly and safely as possible from public areas.
Some parts of the Albany Megacentre were still closed because of tornado damage and police said motorists should expect some disruption near the Megacentre.
