More rain to follow in the wake of storm month

April's weather was notable for a 1 -hour thunderstorm which unleashed record rainfall on parts of Nelson, leading to devastating flooding in pockets of the region.

The month was also marked by 79 per cent more rainfall than average, resulting in 15 per cent fewer sunshine hours than average, John Mathieson of Nelson Weather said.

Rainfall figures compiled by the service showed that on the day of the storm, April 21, Riwaka had 134mm of rain, Richmond east 192.6mm, Ngawhatu Orphanage stream, 180mm, Waimea West 191mm, Nelson Airport 121mm Stoke south 125.3mm, Stoke north 59.6mm, Tahunanui 55mm, Nelson City 33.3mm.

Most rainfall recorded over the 24-hour period fell during the 1 -hour thunderstorm centred over Monaco to Suffolk Rd and Richmond between 5pm and 7pm, Mr Mathieson said.

"An example of maximum one hour rainfall was 75mm recorded at Kingsley place, Richmond east from 5pm to 6pm.

"The most active sector of the rain band associated with this thunderstorm placed just southwest and south of Tahunanui and northern Stoke," Mr Mathieson said.

Nelson City and the Tahunanui hills were spared the worst and received little more than passing showers near the periphery of the "vigorous cloudburst", he said.

The MetService said after a break today, more rain was forecast for Nelson tomorrow, with a southwest change.

A rapidly evolving weather system is expected to arrive from the Tasman Sea, bringing a wet end to the week over most of New Zealand, especially central areas, meteorologist Daniel Corbett said.

"This approaching weather system will linger across central New Zealand over the next couple of days. Persistent and at times heavy rain is likely over central areas," he said.

The "lingering low" to the west of the North Island will cause the front to stall, causing heavy rain in parts of Nelson, especially over the hills and ranges, Mr Corbett said.

A surge of much colder air is expected to follow with "wintry air" likely to drop snow down to very low levels across the far south of the South Island, Mr Corbett said.

The Nelson Mail