"Out at sea they can look a lot more dramatic because they suck up all the water."
There remained a low to moderate risk of small tornadoes in western parts of the country.
Earlier, the MetSevice issued a severe thunderstorm outlook for Northland, Auckland, the Coromandel Peninsula, Waikato, Waitomo, Taranaki, Bay of Plenty, northern Gisborne, Buller and Nelson.
MetService meteorologist Daniel Corbett said 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.
Mr Duncan said further land-based tornadoes were most likely to hit rural areas.
The public were 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."
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.
