Heavy weather ahead for much of the South Island, Wellington and Wairarapa

Weather warnings and watches cover most of the country from Wellington south for the next 24 hours, including a heavy swell warning for Wellington and Wairarapa and heavy rain in Dunedin.

MetService issued Severe Weather Warnings for heavy rain and severe gales from Monday through to early Wednesday. Waves of up to 5 metres are expected off the Wellington coast overnight on Tuesday, and up to 6m in Wairarapa.

“The active weather has already begun on the West Coast today (Monday) where a front is delivering heavy rain,” MetService Meteorologist Jessie Owen said.

“Thunderstorms are embedded within this front, contributing to the high rainfall rates and producing lots of lightning.”

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A strong northwesterly flow would be followed by a strong, cold southerly change.

The South Island is being hit by a one-two punch, with a front on Monday bringing heavy thundery rain to Westland and Fiordland, along with a chance of heavy and thundery rain in Otago and Southland on Monday night.

Then on Tuesday, MetService expects a cold southerly change to move up the east of the island, bringing heavy rain to some easterly areas, and large swells to the coast.

“A noticeable drop in temperatures will be felt across the South Island on Tuesday (and the North Island on Wednesday) following the southerly change,” Owen said.

“Overnight temperatures are set to plummet through the single digits; Alexandra, Wanaka, and Queenstown are forecast to drop to 3°C overnight Tuesday, Taumarunui can expect 3°C and Taupō 4°C overnight Wednesday.”

Christchurch is forecast to have northerlies and increasing cloud on Monday, then some heavy rain on Tuesday, along with strong to gale southwesterlies. The city is expected to only reach the low teens Tuesday afternoon.

MetService is warning of a risk of heavy rain in Dunedin between 11pm Monday and 11am Tuesday, with a possibility as much as 90mm could fall.

There’s also a heavy rain warning for Southland and the Clutha area in the 12 hours from 8pm Monday.

Police advised people in Otago and Southern districts to avoid unnecessary travel and if possible stay indoors. Areas between Balcutha, and Waikouaiti were likely to experience the most rain.

The North Island should mostly avoid the bad weather, apart from strong winds in Wellington and southern Wairarapa overnight Monday, when severe northwest gales could gust to 120kph in exposed places. There’s also a chance of heavy rain in the Tararua Range Tuesday morning.

Tuesday looks likely to be a scrappy day in Wellington, with a few showers, along with strong northwesterlies turning southerly later.

Snow lowering to about 1000 metres is forecast for the Canterbury High Country on Tuesday, and in parts of Otago excluding Dunedin and Clutha.

Other places with heavy rain warnings at some point on Monday or into early Tuesday are Fiordland, Westland south of Otira, and the headwaters of the Canterbury lakes and rivers south of Arthur’s Pass.

Among areas covered by a less severe heavy rain watch are the Canterbury Plains and Banks Peninsula in the 24 hours from 9am Tuesday, and Otago, excluding Clutha and Dunedin on Tuesday morning.

In the South Island, severe gusts to 120kph in exposed places are forecast for Marlborough overnight Monday, the Canterbury High Country from 3pm Monday to 6am Tuesday, and Banks Peninsula from noon Tuesday to 9am Wednesday.