An Aucklander has captured a mesocyclone that weather forecasters have described as "really unusual".
Newshub was sent a photo by a member of the public taken on Tuesday evening of a cloud formation that had similarities to a doughnut.
NIWA forecaster Ben Noll told Newshub it was a mesocyclone, which he described as a "vortex of air, typically 5-15km in diameter and existing within a heavy shower or thunderstorm".
"In a mesocyclone, air rises and rotates around a vertical axis. The feature spotted on Tuesday evening was likely contributed to by wind shear, or the change of wind speed and direction and direction with height, which produces the spin needed to get them going," Noll told Newshub.
"This one was probably due to a combination of decaying afternoon sea breezes, Auckland's varied terrain, and a heavy shower in the vicinity causing localised wind shifts."
Philip Duncan from WeatherWatch believed the cloud formation was "really unusual" and was caused by Auckland's weather conditions on Tuesday evening.
"Yesterday Auckland had instability caused by moisture in the atmosphere, winds converging over the city and daytime heating," Duncan explained.
"In fact, Auckland was several degrees above normal yesterday, producing some lumpy cloud build-ups and isolated heavy showers."
Duncan believes it's possible the clouds were starting to rotate a little, which he described as a "large and lazy vortex" in the sky caused by the terrain below but stressed it wasn't a tornado.
But MetService's Lewis Ferris said it's hard to determine what the cloud formation was from a single image but added the light and dark areas give it an "interesting perspective and depth".
"The 'donut' shaped part of the cloud is at the lower level than the more widespread cloud in the picture," Ferris said.
"That's why it looks like it has a halo because some of the sunlight is reflecting off the top of it and illuminating the larger layer of cloud."
He said the cloud looks "lenticular in nature", which he believes is pretty uncommon for Auckland.
"It was a southeasterly wind flow across the area so it's possible that this cloud has formed downwind of the Hunua Ranges which would mean this photo was taken looking approximately eastwards," Ferris explained.
"If the cloud was lenticular in nature then it would have been approximately stationary as lenticular clouds form on 'standing waves' much like water flowing over a boulder in a stream.
Upon viewing the video footage from the NIWA webcam on the skytower, Ferris said his initial hunch about lenticular clouds was wrong because the apparent rotation of the cloud and it travelling along with the wind.
"The circulation in the cloud is related to different low level wind flows around the Auckland region being concentrated by an updraft due to the unstable atmospheric conditions present yesterday. The concentration of the spinning is much like how an iceskater spins faster when they bring their arms closer to their body - it's conservation of angular momentum."
Watch the video of the cloud formation above.
