A severe thunderstorm outlook has been issued by MetService.
There is a moderate risk of thunderstorms, heavy rain and gusts from this afternoon in Northland, Auckland, the Coromandel Peninsula, Waikato, Waitomo, Taranaki, Bay of Plenty, northern Gisborne, Buller and Nelson, said MetService meteorologist Daniel Corbett.
Tornadoes were possible, but unlikely.
"The main risk is for heavy downpours and hail, [but] we can't completely rule out the risk of a tornado," he said.
Some tornadic systems such as funnel clouds, waterspouts and small land-based tornadoes were possible with thunderstorms.
WeatherWatch.co.nz said there was a low to moderate risk of small tornadoes in a zone extending across West Coast, Taranaki, King Country, Waikato, Auckland, Northland and Great Barrier Island.
The risk was immediate for Taranaki over the next few hours, and the risk would increase tonight in Waikato and Auckland.
The existing weather system has produced small tornadoes in the past, said head analyst Philip Duncan.
"If a few form they're most likely to hit rural areas. Please note these tornadoes are nothing like the ones we've seen today in the United States, however even low scale tornadoes can be deadly - as we've seen in Auckland in recent years," he said.
The public were being reminded to keep up to date with the latest weather and conditions, and to keep an eye on the skies.
While the chance of a tornado forming was low to moderate, the chance of a tornado hitting someone's home was "very low", he said.
"Tornado injuries and deaths are often caused by flying debris so stay indoors until storms pass," said Mr Duncan.
Tornadoes in New Zealand
About 20 to 30 tornadoes happen in New Zealand each year, most frequently in the west and north. Tornadoes sometimes occur during thunderstorms, are sometimes preceded by a long, continuous roar or rumble, and generally last less than 15 minutes.
Damage paths are 10 to 20 metres wide and are usually less than five kilometres long.
WHAT TO DO
- Develop a household emergency plan and prepare a portable getaway kit.
- When a warning is issued, alert others if possible.
- Take shelter in a basement or interior room without windows on the lowest floor, and get under sturdy furniture.
- Close windows, external and internal doors.
- Don't walk around outside, and avoid driving unless absolutely necessary.
- After the storm, listen to local radio stations for updates and advice from emergency management officials.
- Ask your council for advice on how to clean up debris safely.
Source: Ministry of Civil Defence and Emergency Management
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