Thunderstorms, hail, downpours in South Island

High intensity heavy rain forecast could cause flash and surface flooding, and rising rivers, the Otago Regional Council warns.

Weather in the South Island is expected to be very unstable this afternoon and evening, causing rain, showers and thunderstorms with localised downpours affecting many inland areas.

A heavy rain watch is in place for Central Otago, North Otago, inland Dunedin and the Clutha from midday to midnight tonight. A severe thunderstorm watch was also in place, including these areas as well as the Southern Lakes and all of Dunedin.

The ORC said this was likely to affect river flows in the Manuherekia, Upper Taieri, and Pomahaka catchments, as well as rivers in the North Otago area.

The level of impact would depend on the location and intensity of downpours; however, there could be surface flooding and rapid and sudden rise of water levels in streams and rivers, resulting in water overtopping river banks, it said.

"Where there are steep and narrow catchments and alluvial fans, for example in and around Roxburgh and Middlemarch, localised severe downpours could trigger the mobilisation of sediments and debris. This can cause blockages that cause streams to break out of their existing channels.

"Rainfall amounts and intensities for these areas will be closely monitored by ORC’s duty flood team. ORC contractors remain available to respond to this event."

MetService said more rain could be expected today for inland Canterbury, south of Fairlie, as well as Central Otago, North Otago, inland Dunedin, Clutha and also Southland, north of Gore.

Thunderstorms about the Canterbury foothills, inland parts of South Canterbury, Otago, northern Southland and inland Fiordland could be severe, producing localised downpours of 25 to 40 mm per hour. 

"Rainfall rates of this intensity will cause surface and/or flash flooding, especially about the hills and ranges and other areas affected by the recent flooding, and could also cause problems for people travelling through these regions."

Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain.

- By John Lewis and ODT Online 

 

 

 

 

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