Photo: MetService
Severe thunderstorms have been detected near Cave, the Hunters Hills and Albury in inland Canterbury, with showers and rain forecast for much of the country for the next few days.
MetService says the thunderstorms are moving northeast and will also affect Fairlie and Beautiful Valley. They are expected to be accompanied by torrential rain and hail.
The forecaster is warning people to watch for surface and flash flooding, and that driving conditions may be extremely hazardous in the area.
A Severe Thunderstom Warning has been lifted for the Cantebury area, however, a Severe Thunderstorm Watch remains in force for Marlborough, the Canterbury plains and high country, North Otago, Central Otago and Dunedin.
For eastern parts of Marlborough and inland parts of Canterbury and Otago a few thunderstorms could be severe between 2pm and 9pm on Monday, producing localised downpours of 25 to 40 mm/h.
MetService meteorologist Oscar Chiviti said there were similar weather patterns last weekend.
"We've had showers that have developed into some thunderstorms during the afternoons in the past two days or seen similar instances where some of the showers have significant thunderstorms with them, which then leads to some localised flooding as well as other impacts."
Chiviti said it was too hard to pinpoint where the latest bad weather could hit the hardest.
"I think once we start seeing those first pings of thunderstorms developing, then that's where we can highlight the areas in the vicinity of where the thunderstorms develop."
There was a risk of flooding in low-lying areas.
"We're expecting in areas for the rainfall to be between 25 to 40mm of rain per hour, so if that does happen, that means flash flooding is most likely in those areas."
He said the weather could be wet on Christmas Day.
"So for Christmas Day, we're expecting this front to start making its way into the western half of the South Island.
"The area we're expecting the first indication of rain would be Fiordland overnight into the morning of Christmas Day.
"And then during the morning period, [we're] expecting that rain to slowly move upwards over the South Island in the west, so as the day progresses in the afternoon and evening, we're expecting the western half of the North Island as well to start seeing some of that rain and then moving over to the central and eastern half.
"But then I should say for the most part on Christmas Day, the eastern half of the country will have fine spells, it's only late in the evening where some of that rain might spill over into the eastern areas," Chiviti said.
The best of the weather in the lead-up to Christmas Day looks to be on Tuesday.
MetService is forecasting dry weather for most of the country, though Fiordland gets rain in the evening.
Rain or showers continue on Boxing Day - and the weather stays wet on Friday.