Rivers across the region are on the decline and rainfall is easing.

West Coast Group Controller, Te Aroha Cook, said that the forecast rainfall totals had not eventuated for the West Coast, however, had affected the top of the South Island, and Nelson.

“Some of the partner agency support staff surged into the region to assist in the lead up to the weather are now being deployed to assist Nelson/Tasman.”

Reports from West Coast Regional Council Hydrology noted that intensities did not reach river levels of concern. The Mokihinui and Karamea Rivers peaked overnight and are now below warning levels. For the Buller River, upper catchment levels appear to have peaked and are now declining steadily. Te Kuha peaked overnight, and it is unlikely rainfall received today will result in flows to be concerned for downstream.

In Westland, there is steady rainfall about the Hokitika River catchment which is keeping the flows above normal. There does not appear to be enough rainfall to see any rapid rates of rise. However, it is noted that there may be another small peak seen later today. The Waiho River is holding around 7m with a slight rise expected today in response to further rainfall. The Haast River remains well below its first alarm level. While there has been some increase in flows, the forecasted rainfall is unlikely to see it reaching flows of concern. Localised rainfall is being monitored across South Westland with the likelihood of thunderstorms through to this evening.

Ms Cook noted that there is a further period of heavy rain expected over the weekend.

“Emergency Operation Centres across the region, and the Emergency Coordination Centre, will continue to be staffed.”

“With saturated soils and some full rivers, we need to keep a close eye on what this next weather system may bring. While we have some crews moving north, we also have capacity here to respond should we need to over the coming days.”

Strong wind and rain warnings remain in place.

Heavy Rain Warning - Red

Impact: This rain is expected to cause dangerous river conditions and significant flooding. Slips and floodwaters are likely to disrupt travel, making some roads impassable and possibly isolating communities.

Area: Buller

Period: 12hrs from 9am - 9pm Thu, 18 Aug

Forecast: Expect a further 70 to 100 mm of rain to accumulate about the ranges south of Little Wanganui on top of what has already fallen, and 30 to 70 mm elsewhere. Peak rates of 10 to 15 mm/h about the ranges. Note, heavy rain is forecast to return Friday afternoon, then ease Saturday afternoon. This next period of rain will exceed warning criteria, and probably lead to more surface flooding and slips due to the ground already being saturated from recent heavy rain. In the 24 hours from Noon Friday to Noon Saturday, expect 80 to 130 mm to accumulate about the ranges. Peak rates of 15 to 25 mm/h.

Area: Westland

Period: 13hrs from 9am - 10pm Thu, 18 Aug

Forecast: Expect a further 120 to 160 mm of rain to accumulate about the ranges on top of what has already fallen, especially between Bruce Bay and Otira, and 30 to 60 mm about the coast. Peak rates of 10 to 20 mm/h about the ranges. Thunderstorms possible about the ranges south of Ross this afternoon and evening with localised rainfall rates up to 25 mm/h. Note, heavy rain is forecast to return Friday afternoon, then ease Saturday afternoon. This next period of rain may exceed warning criteria, and could lead to more surface flooding and slips due to the ground already being saturated from recent heavy rain. From the glaciers northwards, in the 24 hours from Noon Friday to Noon Saturday, expect 80 to 120 mm to accumulate about the ranges. Peak rates of 15 to 25 mm/h.

Strong Wind Watch

Area: Nelson, Tasman and Buller

Period: 9hrs from 9am - 6pm Thu, 18 Aug

Forecast: Northeast winds may approach severe gale at times. Winds easing in Buller early afternoon.

You can keep up to date with the latest information by:

• following the West Coast Emergency Management Facebook page
• checking state highway conditions at https://www.journeys.nzta.govt.nz/traffic/southisland
• monitoring weather conditions at https://www.metservice.com/warnings/home

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