Westland is in for up to 800mm of rain over the next few days. Photo: RNZ / Tess Brunton
Orange rain warnings in place for Tuesday have now been extended to cover the Canterbury High Country.
The MetService warnings now cover Westland south of Hokitika from 9am-6pm Tuesday, Fiordland about and north of George Sound from 4am Tuesday to 3am Wednesday, the headwaters of the Canterbury lakes and rivers south of Arthurs Pass from 3pm Tuesday to 5pm Thursday, and the headwaters of the Otago lakes and rivers from 9am Tuesday to 8am Wednesday.
In addition, heavy rain watches are in place for the Grey district and Westland about and north of Hokitika from 6pm Tuesday to 6pm Thursday, and Fiordland south of George Sound from 4am-9pm Tuesday.
Strong wind watches are in place for Fiordland from 8pm Monday to 6pm Tuesday and the Canterbury High Country from 12pm Tuesday to 12pm Wednesday.
The major weather system is set to bring days of heavy rain and strong winds, with "significant" rainfall of up to 800mm expected to accumulate around the Westland ranges.
MetService said there was the potential for Westland to be upgraded to a red warning over the coming days.
Red weather warnings are only used for the most severe storms, such as Cyclone Gabrielle in 2023.
The forecaster said it only issued red warnings when it expected widespread significant impacts, disruptions or safety issues.
The vast majority of red warnings issued since their introduction in 2019 have resulted in local or regional states of emergency being declared.
However, MetService said there was "some uncertainty" about the weather system's movement and "the placement of heaviest rain may change".
People were advised to keep up to date with the latest forecasts.
The forecaster warned that heavy rain could cause streams and rivers to rise rapidly.
"Surface flooding and slips are also possible and driving conditions may be hazardous."
Westland prepares for deluge
Local civil defence is taking a precautionary approach as Westland prepares for a deluge, with plenty of visitors still in the area.
West Coast Emergency Management said it had not ruled out activating an emergency operation centre if needed.
Group manager Claire Brown said large rainfall was no stranger to the West Coast, but people needed to take care.
"We're also concerned about the duration of the event. So this is over quite a number of days and also because the Westland area has been affected ... we have a number of people in the community who are quite rightly concerned and worried about could happen over the next couple of days."
There was still "quite a volume" of tourists in the region, and she encouraged them to check the MetService, NZ Transport Agency and West Coast Emergency Management web pages to stay across any developments.
People in the area should keep up to date with the latest information and take precautions, she said.
That included reviewing emergency plans for their home or work and ensuring travellers had water, food and warm clothing with them.
An inter-agency briefing would be held on Tuesday morning so local officials could get an forecast update, check preparations, where they might need to send resources and plan for what might happen over the next few days.
"We're always thinking about the 'what if?' What if we do need to be in a position where we need to evacuate people or move people to safe areas so that type of thinking is always a part of the planning and preparedness conversation," she said.