Weather: Heavy rain warning expected as West Coast braces for downpours; forecasters warn half a metre of rainfall at altitude

An orange heavy rain warning is expected to be issued for the South Island’s West Coast ahead of a mid-week deluge, with forecasters warning of half a metre of rain at altitude.

The source is a plume of tropical moisture set to strike the South Island from Wednesday, delivering rain to western and southern areas.

Auckland, meanwhile, should see cloudy periods and the chance of a shower in the west this afternoon. It was expected to hit 19C today and tomorrow, before rising to 22C over the weekend.

Heavier rain is forecast for Auckland’s long weekend.

A heavy rain watch has already been issued for Fiordland, north of Doubtful Sound, by forecaster MetService for 30 hours from 9am on Wednesday.

“Heavy rain is expected and amounts are likely to exceed warning criteria,” MetService said, adding there was a “high chance” the warning would be upgraded.

MetService meteorologist Dom Barry said a series of weak fronts would be tracking up the South Island from Wednesday and more watches or warnings for other areas were likely to be issued.

A quick look into the expected weather for the next three days. Lots of sunshine to look forward to in the east ☀🌞whereas cloud expected to increase from the south and moving up Aotearoa/New Zealand in the west and also affecting central areas 🌤☁ Rain expected in the south,… pic.twitter.com/gZnYCek0f6

— MetService (@MetService) October 21, 2024

Barry said some parts of the West Coast would “easily” see half a metre of rain at higher elevations in the next 10 days or less.

“There most certainly is going to be heavy rain at sea level,” he said.

Barry said the wettest days for the country looked to be Wednesday and Thursday, with western and southern areas of the South Island in the firing line.

The “warm and moist” northwesterlies developing over the South Island would also bring warmer temperatures, Barry said, with eastern parts of the country set to see higher-than-average minimum and maximum temperatures later this week.

Another half metre + rainfall event on the cards for South Island's west coast this week. A Tasman cut off low will drag down tropical moisture delivering 2 moisture plumes in the next 7 days. The 2nd will also deliver heavy periods of rain for the North Island on Saturday. pic.twitter.com/vymHr3oxUZ

— Hauraki Gulf Weather (@HaurakiGulfWx) October 20, 2024

“For the easternmost places like Christchurch, Oamaru, Napier and Hastings, maximums in the mid-20s can be expected. Overnight temperatures will stay warm as well, in some cases only being a couple of degrees cooler than the day’s maximum, which might make sleeping a struggle for some,” Barry said.

MetService predicts highs of 26C to 27C in Hawke’s Bay on Thursday and Friday – Hawke’s Bay Anniversary day – and lows of 13C and 16C.

However, rain and wind are set to return elsewhere, bringing gloomy conditions for parts over the long weekend.

“Low pressure is returning at the end of this week, meaning some wetter weather is in store over the long weekend. With some drier weather possible for Labour Day, it is worth checking the forecast to get the best out of the weekend,” Barry said.

MetService said a large trough of low pressure was likely to cover much of New Zealand on Saturday, with northerlies affecting the North Island and southerlies developing over the South Island.

☀️ -> 🌧️

A mostly dry start to the week, thanks to a ridge of high pressure, but don't get too comfortable – the weather’s taking a turn by midweek! 🌦️

Showers are set to develop along the West Coast on Wednesday with the potential for heavy rain from Thursday 🌧️☔ pic.twitter.com/iyegoG4JBn

— NIWA Weather (@NiwaWeather) October 20, 2024

“There’s considerable uncertainty regarding the areas most affected, however, heavy rain could affect many parts of the country.

“Consequently, there is low confidence that heavy northerly rain could reach warning criteria about eastern Bay of Plenty, Waitomo, Taumarunui, Taranaki, Kāpiti [including the Tararua range], Wellington, Marlborough, Nelson/Tasman and northern Buller.

“There is also low confidence that heavy south or southeasterly rain could affect eastern parts of the South Island from eastern Marlborough to Clutha.”

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