Heavy black clouds, thunder and a downpour which brought 13mm of rain to one site in the ranges north of Napier on Sunday afternoon was the first sign of a storm forecast for overnight.
A MetService spokesman said about 4.30pm the severe weather warning remained in place, with forecasts of 75mm to 100mm of rain in some places from Tutira north, at up to 35mm an hour in isolated places.
The warning, for the 15 hours from 6pm to 9am Monday would reviewed in the early evening, he said.
MetService warned that heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.