Niwa said an incredible 62.4mm of rain fell between 8am and 9am this morning - the wettest hour in at least eight years - as the slow-moving storm cell delivered a deluge over the northern suburb of Rosedale.
Two motorists needed rescuing from their vehicles after they became submerged in the waist-deep floodwater.
About 14 homes were affected by flooding and firefighters cleared blocked drains to help the water drain away.
Forecaster Tom Adams said much of the North Island remained under a thunderstorm watch until at least 8pm.
He said similar super-sized downpours on localised areas were likely as there was little wind to move the storms away.
"There's not a lot of wind around so when a thunderstorm forms they will stay on one spot. The bad news is that there will be large amounts of rain over one spot."
He warned there was a risk of severe thunderstorms for the rest of the day.
"There are no other cells over the Auckland region but there's lots of opportunity for another two, three or four storms to pop up," said Adams.
A Severe Thunderstorm Watch remains in force for Northland, Auckland, Great Barrier Island, the Coromandel Peninsula, Waikato and the Bay of Plenty.
The Ministry of Civil Defence and Emergency Management advises that as storms approach you should:
- Take shelter, preferably indoors away from windows;
- Avoid sheltering under trees, if outside;
- Move cars under cover or away from trees;
- Secure any loose objects around your property;
- Check that drains and gutters are clear;
- Be ready to slow down or stop, if driving.
During and after the storm, you should also:
- Beware of fallen trees and power lines;
- Avoid streams and drains as you may be swept away in flash flooding.
