MetService is forecasting a significant weather event to unfold over the coming week, which looks set to bring heavy rain and strong winds to many parts of Aotearoa New Zealand, including Otago and the Canterbury High Country.

The heavy rain is expected first over the western South Island from tomorrow (Tuesday), then spreads to the eastern South Island midweek, reaching the North Island by the end of the week.

This sharp pivot will be a marked change after what has been a relatively calm few weeks, a media statement from Metservice said.

The weather system moves onto Fiordland early tomorrow morning and becomes slow-moving in Westland on Wednesday and Thursday, delivering a lot of rain to the area. 

Numerous weather watches and warnings have been issued for heavy rain, including for the headwaters of Canterbury lakes and rivers for the 30 hours from 12 noon tomorrow to 6pm on Wednesday.

Rainfall amounts may approach warning criteria within 15km east of the main divide. A strong wind watch is also in place for the same period, in the Canterbury High Country, MetService meteorologist Mmathapelo Makgabutlane said.

“The ranges of the Westland District south of Hokitika, which are under an Orange Warning, can expect rainfall amounts of 600mm to 800mm between Tuesday and Thursday, with lesser amounts near the coast.

“This is a significant heavy rain event, and we will be keeping a close eye on developments over the next 24 hours as there is the potential to upgrade to a Red Warning,” Mmathapelo said. 

“Rain of this amount may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.”

Other areas in the South Island are also under Orange Warning or Watch, which may be upgraded in the coming days. 

The rain extends northwards to the top of the South Island from Thursday and onto the North Island Thursday into Friday.

“While it’s still early days, there is the potential for heavy rain for places like Tasman, as well as the central North Island. In fact, the whole northern half of the North Island, including Auckland and Northland could be in line for a period of heavier falls as the system moves through on Friday,” she said.

The system also spreads rain eastwards to potentially affect Southland, Otago and Canterbury by the end of the working week.

“This is an evolving situation and is a large weather system with a widespread reach, and anywhere under a Watch, Warning, or highlighted in the Severe Weather Outlook should brace for a wet few days,” she said.

Several other areas across the country may be in line for some strong winds this week, and large waves across the western and eastern coastlines of the South Island are likely on Thursday and Friday as a result of the strong winds and low pressure associated with this weather system combined with the King Tides.

“Wherever you are in Aotearoa New Zealand this week, be sure to keep an eye on the weather, as this system will affect all parts of the country to varying degrees,” Mmathapelo said.