Metservice says the already-battered central Otago is also set to get more wild weather.
More dramatic thunderstorms are expected to roll across the central and lower North Island and inland areas in the South Island today.
Sporadic but heavy showers and isolated thunderstorms are forecast for the afternoon and will last into the evening, according to MetService.
Central Otago town is bracing itself for more wet weather as residents continue cleaning up after a flash flood only two days ago.
Heavy downpours caught Roxburgh locals by surprise on Sunday afternoon as a MetService weather station recorded almost 30mm of rain in one hour and a temperature plummet of 5C.
The flash flood sparked evacuations and cut off power and water. Residents have been told to expect to be without water until at least tomorrow.
Evacuations in Roxburgh on Sunday afternoon were shortlived but the town remained cut off from the South because of slips on State Highway 8 and Teviot Rd.
The Central Otago District Council issued a boil water notice for the area after a water pipe blew out. They were also asking residents in the area to conserve water overnight.
In a post on the council's Facebook page yesterday afternoon Mayor Tim Cadogan congratulated locals on their clean-up efforts and community spirit.
"It was amazing being there today and seeing people getting stuck in, caring for their neighbours, shovelling silt, getting water containers to those who couldn't get it themselves, making meals for those in need and so forth.
"This is rural New Zealand at our absolute best."
Another post last night warned locals in neighbouring towns Clyde and Alexandra of further flooding, slips and other hazardous conditions caused by ongoing rain.
"There is surface flooding in several places, please stay off the roads until this passes and the water's drained away," the post said.
A thunderstorm outlook on MetService said storms across these southern regions could today produce rainfall of 10 to 25mm an hour as well as hail. There was a moderate risk of severe thunderstorms, which would produce localised downpours of 25 to 40mm an hour.
Thundery, wet weather is expected to hit the lower North Island and inland parts of the South Island later today. Photo / Metservice
Further north, thunderstorms from the ranges of Wairarapa and Hawke's Bay to Inland Taranaki could produce localised rain of 10 to 25mm per hour.
There was also a moderate risk of severe thunderstorms, which could cause flash flooding, slips and hazardous driving conditions.
