'Bomb cyclone' to hit B.C.'s South Coast, wind warnings issued

UPDATE — Monday, Sept. 25: Wind and rainfall warnings, ferry sailings cancelled as storm moves over B.C. coast

A large storm system is on its way to coastal British Columbia on Sunday, prompting high streamflow advisories, wind warnings and concerns for potential power outages and flooding over the next few days.

A "bomb cyclone" — a low-pressure system that brings rain and powerful winds — is expected to hit offshore close to Vancouver Island and pick up through Sunday afternoon, according to Environment Canada.

The agency forecasts more than 50 millimetres of rain will hit western parts of Vancouver Island by Tuesday, while Metro Vancouver and other parts of the southern coast will get closer to 30 millimetres.

The forecast has prompted the provincial River Forecast Centre to issue a high streamflow advisory for Vancouver Island, the Sunshine Coast, Howe Sound and the Lower Mainland.

But experts say B.C. isn't likely to see flooding anywhere near as devastating as the series of atmospheric rivers in November 2021 that washed out highways and caused large areas of cities including Abbotsford, Chilliwack and Merritt to be submerged.

"It's mostly going to be a wind event with this storm and [it] is also going to bring some rain but not warning level amounts of rains," said Louis Kohanyi, a meteorologist with Environment Canada. 

"We're looking at the winds gusting 80 to 100 km/h, and it's going to be even windier for north Vancouver Island."

The forecaster has issued a wind warning for parts of the Sunshine Coast and the north, east and western portions of Vancouver Island on Sunday.

A special weather statement also warns of strong winds on the southern tip of the island, with Environment Canada saying the "significant fall storm" means it will remain windy on Monday. 

B.C. residents should be prepared for high winds and fallen trees to cause potential power outages, with spare batteries, candles, non perishable food and clean water, said Brent Ward, co-director of Simon Fraser University's Centre for Natural Hazard Studies.

Some vulnerability to flooding

While rain is welcome amid historic drought conditions and wildfires across B.C., Environment Canada says there won't be enough in the north and Interior to completely douse wildfires.

And experts say the heavy rainfall carries flooding risks for already damaged ecosystems on Vancouver Island and across the southern coast.

Ward said B.C. could see localized flooding in some areas, particularly on Metro Vancouver's North Shore in areas like Mosquito Creek and McKay Creek — where water levels can rise quite quickly.

"Because we haven't had a lot of rain in a long time, some culverts might plug around roadways," said Ward. "So you could easily see pooling water on the road surface, which is always a concern."

"I don't think we're going to have enough water to actually trigger landslides. So that's good news," he added.

Drought and wildfire exacerbate one another, leaving soil not only parched but also much less absorbent to water when it does fall, said Daniel Sharp, an arborist with Davey Tree Service in Vancouver.

They also damage vegetation and trees, making root systems less stable and trees more likely to fall over or be washed away, he added.

"The reduction in plant matter is going to mean that the water that comes down … those hillsides are going to have nothing to absorb it," said Sharp. "That's when you potentially see things like landslides and flooding in those recently burned areas."

Trees that fall can also down power lines and cause widespread outages, said Sharp, or accumulate and block water drainage, making flooding worse.

B.C. Hydro said in a statement about half of all power outages are caused by fallen trees, and it's watching out for more this weekend.

But Ward says the rain is good news, not least for fish whose spawning cycles have been disrupted by lower water levels in several rivers and lakes this past summer.