Flood watch issued on B.C.'s South Coast as atmospheric river approaches

The B.C. River Forecast Centre has issued a flood watch for much of the South Coast and all of Vancouver Island as "a series of potent storms" approaches the region.

The flood watch was issued Thursday afternoon for Howe Sound, the Sunshine Coast, the Sea-to-Sky region and the North Shore mountains, along with the "Fraser Valley – North" region, which includes tributaries of the Fraser River from Port Coquitlam to Harrison.

The rest of the lower Fraser River basin is under a high streamflow advisory.

"A series of potent storms is forecast to impact coastal British Columbia this weekend and next week, with an initial storm Friday, again on Saturday-Sunday, and another into Monday," the river forecast centre's statement reads.

"Current forecasting is indicating the strongest atmospheric river event making landfall on Monday, with the potential for additional rainfall in the middle of next week."

The centre said the heaviest rainfall is forecast over West Vancouver Island and the Coast Mountains, with total rainfall from Saturday to Wednesday expected to be 200 to 300 millimetres. Some areas could see as much as 400 millimetres.

Other parts of the region are expected to receive between 70 and 250 millimetres of rain, and warm temperatures are expected to lead to snowmelt at "lower and mid-elevations," according to the forecast centre.

"Rivers are expected to rise over the weekend and into next week," the statement reads. "Peak river levels are expected to occur in most areas on Sunday to Tuesday and may extend from Tuesday to Thursday for lake-driven rivers."

The centre says its modelling shows "a high likelihood for moderate flood conditions" in the areas with the heaviest rainfall, as well as "a chance that more severe flooding could occur."

B.C.'s Ministry of Transportation and Infrastructure says its staff and contractors will be working around the clock with enhanced protocols.

Areas being closely monitored are:

• Highway 4 at Cameron Lake on Vancouver Island
• Highway 1 in the Fraser Valley near Bridal Falls
• Highways and bridges on the Sunshine Coast, along Howe Sound/Sea to Sky Highway, and in the Pemberton Valley

"There remains uncertainty over the amounts of rainfall that will occur and the locations of heaviest rainfall," the statement reads, noting that the changes to the storms' tracks from the current forecast could change which areas are most affected.

In its own statement Thursday night, B.C.'s Ministry of Emergency Management and Climate Readiness urged people to prepare for potential flooding, power outages and landslides.

"While the forecast for wet and stormy weather is seasonally typical, the province is monitoring conditions closely, working directly with communities on preparedness activities, and prepared to deploy as many as four million sandbags and other flood-related emergency-response strategies if needed," the ministry said.

The ministry urged people to stay away from river shorelines, avoid driving through floodwater and to prepare their households for evacuation, if necessary.

The City of Vancouver says crews have been out making sure catch basins on priority routes and areas prone to flooding are clear to allow drainage.

There are 45,000 catch basins across Vancouver.

Residents are asked to call 311 if flooding on city property is noticed. 

Detailed information on how to prepare for flooding can be found on the provincial government's website.  

High streamflow advisories mean "river levels are rising or expected to rise rapidly," but "no major flooding is expected."

Flood watches, by contrast, indicate that "river levels are rising and will approach or may exceed bankfull."

The forecast centre issues a flood warning when "river levels have exceeded bankfull or will exceed bankfull imminently" and flooding of adjacent areas will occur. 

With files from CTV News Vancouver's Abigail Turner