Forecaster WeatherWatch admits it had no idea what the strange rays were that appeared on the horizon off Gisborne.
Pictures of the phenomenon were sent in by WeatherWatch.co.nz reader Anna Powell.
WeatherWatch was "stumped" by the images and sent them to meteorologist Brandon Miller, of CNN America, who said the effect was caused by sunlight and moving cloud shadows.
"The light rays are actually parallel to each other, but they appear to converge on the horizon. The same optical illusion ... makes parallel train tracks appear to converge on the horizon," he said.
"These are similar to the more familiar 'crepuscular rays' but they are opposite the sun in the sky and since you cannot see the sun in this picture, it is likely above or behind the camera these would be anticrepuscular. Crepuscular rays radiate directly from the sun, which is often obscured by a cloud, revealing only the rays."