A month's worth of rain fell on Wanganui in one day during the flood that swamped large parts of the city.
Meteorologist Emma Blades said that on Friday and Saturday 138mm of rain fell at Wanganui Airport, and of that, 90mm fell on Saturday alone.
"The average June rainfall for Wanganui is 94mm, so that was a very heavy period of rain."
Ms Blades said the heavy rain was caused by the same weather system that brought flooding to Hokitika last week.
"It was a really warm, moist north-west flow, and the warmer it is the more moisture it holds. It was very slow moving."