MetService has issued a severe thunderstorm watch for much of the east coast of the South Island for today.
The watch covers Marlborough, Canterbury Plains, Canterbury High Country, North Otago, Central Otago, Dunedin and Clutha.
A few thunderstorms in these areas could be severe between 2pm and 9pm today, producing localised downpours of 25 to 40 mm/h.
After the watch was issued, severe thunderstorms were detected near Cave, the Hunters Hills and Albury in inland Canterbury.
MetService said the thunderstorms were moving northeast and would also affect Fairlie and Beautiful Valley. They were expected to be accompanied by torrential rain and hail.
The forecaster said rainfall of the expected intensity could cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips.
MetService earlier intimated that barbecues might not be in order on Christmas Day and Boxing Day in Dunedin and most of Otago, as rain is expected on both days.
MetService forecaster Surprise Mhlongo said there should be some fine patches during Christmas morning, but a "short front" from the west arriving later in the day would bring spotty rain until the evening.
"So if you’re planning to be outside most of Christmas and Boxing days, you could be disappointed."
Dunedin was expected to reach a high of 19°C on Christmas Day, and 18°C on Boxing Day.
For those staying in Alexandra and Queenstown, their Christmas and Boxing Day weather was likely to be slightly more settled, as temperatures were expected to peak at 26°C in Alexandra and 23°C in Queenstown.
Oamaru and Invercargill would also begin the festive season with a mixed bag of weather, reaching highs of 19°C and 21°C respectively on Christmas Day, and showers on Boxing Day.
