Severe thunderstorms for Westland, heavy rain warnings for Southland and Otago

An orange level heavy rain warning is in place for parts of the central and southern South Island through to Wednesday morning.

A severe thunderstorm warning is in place for the Westland, Selwyn, Ashburton, Timaru and Mackenzie .

Severe thunderstorms are moving east and expected to lie near Harihari and Lake Ianthe at 6.15pm Monday, MetService said.

They are expected to be accompanied by torrential rain and damaging wind gusts.

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

Very strong wind gusts can break branches from trees, damage roofing, and make driving hazardous especially for high-sided vehicles and motorcycles, it said.

Heavy rain

An orange level heavy rain warning is in place for parts of central and southern New Zealand through to Wednesday morning.

The rain may cause streams and rivers to rise rapidly, and cause surface flooding and slips.

The headwaters of the Canterbury lakes and rivers about and south of Arthur’s Pass can expect 110 to 160 mm of rain on the main divide, and 70 to 110 mm within 15 km east of the divide through to midnight Monday.

Westland about and south of Otira, through to 7am Tuesday, can expect 210 to 260 mm of rain to accumulate about the ranges, and 70 to 120 mm near the coast. Peak rainfall rates of 25 to 40 mm/h this afternoon and evening about the ranges.

From 8pm Monday through to 8am Tuesday Southland and Clutha can expect 60 to 90 mm of rain, with peak rainfall rates of 10 to 25 mm/h.

The largest accumulations and hourly rainfall rates are most likely to occur about and north of a line from Balclutha to Nightcaps, MetService said.

While Otago celebrates its Anniversary Day today, a heads-up of the heavy rain on the way

Some parts (especially those under a Warning) could get 60 – 90 mm in 12 hrs from tonight

This may bring localised surface floods and hazardous driving conditionshttps://t.co/qHyE5zzql5 pic.twitter.com/O2Q18srLg1

— MetService (@MetService) March 20, 2023

From 11pm Monday through to 11am Tuesday Dunedin can expect 60 to 90 mm of rain. Peak rainfall rates of 10 to 20 mm/h.

Fiordland through to midnight Monday can expect a further 80 to 120 mm of rain on top of what has already fallen. Peak rainfall rates of 15 to 25 mm/h.

Thunderstorms were possible in all areas other than Dunedin, MetService forecasts.

Southern Police advised people in Otago and Southern Districts to avoid any unnecessary travel and if possible, stay indoors.

Strong winds

An orange level strong wind warning has been issued for Wellington and Wairarapa south of Masterton until 8am Tuesday, Malborough and Canterbury High Country until 6am Tuesday and Banks Peninsula from noon Tuesday through to 9am Wednesday.

Gusts are forecast to reach 120km/hr in all places.