A "low level jet" is responsible for the deluge inflicted upon West Aucklanders today.
And experts are forecasting such events could become more frequent as the climate warms.
About 50 homes were evacuated after a massive storm hit Auckland overnight with areas of Kumeū, Huapai, Rānui, Piha and Henderson Valley experiencing the largest downpours.
It is the most rain to hit Auckland at once since 2017, with 90mm coming down each hour at storm's most ferocious moments.
The National Institute of Water and Atmospheric Research (Niwa), gave its Twitter followers an insight as to how that much rain fell in such a short time, explaining a "low level jet" was to blame.
"This fast-moving ribbon of air in the low levels of the atmosphere (1500 m up) can rapidly transport moisture," the post said.
"Note the low level jet over Auckland was nearly stationary for many hours."
It contributed to Kumeū registering its second wettest day since records began in 1943, recording 201mm in 14 hours from Monday night to Tuesday morning.
Victoria University environment and earth sciences professor James Renwick said such events were becoming more common thanks to climate change, as warmer air could hold more moisture.
"So when there's a storm, there's more water available to fall out of the sky, so the chances of heavy rainfall go up," he said.
"That doesn't mean every storm delivers a record rainfall, but it becomes easier and easier to break rainfall records, as the climate continues to warm."
Niwa hydrodynamics scientist Dr Emily Lane said although some warming could not be avoided, work should be done now to prevent the problem from escalating.
"We are already locked in to some amount of warming but the future could be much worse if we don't act now.
"We need to mitigate the future effects of climate change by reducing our carbon footprint and also work with at-risk communities to help them adapt and cope with the effects of flooding and other climate change impacts in ways that are fair and equitable."