Powerful storm hits Pahiatua, causes flooding

Water rose right up to lap at the doors of Pahiatua New World last Tuesday.

Flash flooding caused ceilings to collapse and shops flooded in two separate downpours in Pahiatua and Dannevirke last week.

More than 50mm of rain was thought to have fallen in 40 minutes over part of Pahiatua (70mm at Mangatainoka) with numerous businesses affected on Tuesday.

Pahiatua New World was closed for about three hours. Owners Jason and Rachel Griggs couldn't give enough praise for the offers of help and staff staying on after shifts to clean up the water.

Branches came down in Pahiatua's Main Street.

"I've never seen rain as intense as that and the wind was like a gale force storm," Jason said. Pahiatua Fire Brigade was kept busy getting water out of shops and checking if people were managing.

St Anthony's School had a ceiling collapse. Motorcycle HQ had water damage, which wrecked four computers. They received offers of help from as far as Dannevirke. Pahiatua Christian Fellowship building's carpets were soaked.

Even the Bush Telegraph building received help from the fire brigade and the community to clear water out.

Roads turned to rivers in Dannevirke last Monday, shops flooded and vehicles were swamped by water as a severe thunderstorm dumped more than 23mm of rain on Dannevirke in less than an hour.

The dramatic thunderstorms were the result of a static weather pattern settling over New Zealand, MetService said.

Derek's Electrical co-owner Kathy Massey had to deal with flooding at the back on High St. Tararua District Council's finance manager left a meeting in the mayor's office to discover knee-high water was flowing through his car on Denmark St. He was unsure what damage had been done to the car's electrical systems. On High St, NZCU Baywide shut early after flooding.

Mesoscale Systems

The burst of intense rain, hail and wind that hit Pahiatua last Tuesday was called a mesoscale convective system (MCS), a complex of thunderstorms organised on a larger scale than the individual thunderstorms but smaller than extratropical cyclones, and normally persist for several hours.

A mesoscale convective system's overall cloud and precipitation pattern may be round or linear. The type that forms during the warm season over land has maximum activity during the late afternoon and evening. A temperature drop from 22 to 14 degrees and 47mm of rainfall was recorded by Philip Morrison in Pahiatua township.