Weather: Saturday soaking for the south

Heavy rain and hail have flooded cars in South Canterbury as thunderstorms sweep though parts of the South Island.

MetService has issued severe thunderstorm warnings for Ashburton and Timaru.

Severe warnings had been in place for Selwyn, Christchurch city, Mackenzie, Central Otago, Waitaki and Dunedin City but have now been lifted.

The regions remain under a severe thunderstorm watch.

Thunderstorms are expected to be accompanied by very heavy rain, large hail and frequent lightning.

"Very heavy rain can cause surface and/or flash flooding about streams, gullies and urban areas, and make driving conditions extremely hazardous," MetService said.

"Large hail can cause significant damage to crops, orchards, vines, glasshouses and vehicles, and make driving conditions hazardous."

The NZ Transport Agency said crews were heading to State Highway Eight between Timaru and Fairlie after cars were flooded by bursts of rain and hail.

A thunderstorm watch is in place for Christchurch, Canterbury Plains, Canterbury High Country, North Otago, Central Otago, Southern Lakes, Dunedin, Clutha, Southland and Fiordland.

MetService said thunder could be accompanied by very heavy rain and large hail.

The watch was expected to be in place until 9pm.

"A cold and unstable air-mass affects the South Island. For much of Fiordland, Southland, Otago, and Canterbury from about Christchurch southwards, there is a moderate risk of thunderstorms this afternoon and evening," MetService said.

"There is also a moderate risk that some of these storms may become SEVERE (sic) between 3pm and 9pm today (Saturday), which could produce localised downpours of 25 to 40mm/h and/or hail larger than 20mm.

"Rainfall of this intensity can cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips."

Poor visibility and surface flooding could make driving difficult, and large hail had the capacity to "cause significant damage to crops, orchards, vines, glasshouses and vehicles".

"Should severe weather approach or if you feel threatened, take shelter immediately."

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