Storm hits Metro Vancouver on Christmas, flood watch issued for Vancouver Island

An atmospheric river brought heavy rain to the Lower Mainland and South Coast on Christmas Day, with authorities saying flooding in low-lying areas could be possible.

Environment Canada has issued a rainfall warning for Metro Vancouver's North Shore, saying that rain is expected to become heavier by Monday afternoon. Around 40 to 60 mm of rain is expected to fall there.

The warnings for the South Coast come after an ongoing windstorm led to warnings up and down the B.C. coast, with gusts of up to 120 km/h prompting warnings from the North Coast, Central Coast and Haida Gwaii all the way down to southern Vancouver Island.

"Hurricane-force winds" have already forced the cancellation of all ferries travelling in the province's north until Dec. 28, with B.C. Ferries promising refunds and even partial reimbursements for those who are affected.

Meanwhile, the B.C. River Forecast Centre has issued a flood watch for the north and west sections of Vancouver Island, following an earlier high streamflow advisory for the South Coast, Lower Mainland and the rest of Vancouver Island due to the storm.

"Current forecasts indicate that the storm will be centred on western and northern Vancouver Island, with likely spillover into southern and eastern Vancouver Island," the advisory reads. "It is possible that heavy precipitation will extend farther inland, up Howe Sound and across the Lower Mainland."

A flood watch is the second in the centre's three-tier flood-warning system. It indicates that river levels are rising and flooding of areas adjacent to swollen rivers may occur. A high streamflow advisory is below a flood watch, and indicates minor flooding in low-lying areas is possible.

Environment Canada has issued rainfall warnings for the north, west and inland sections of Vancouver Island, saying up to 120 mm of rain could combine with the high wind gusts.

The River Forecast Centre said its forecasts indicate river levels are expected to rise quickly on Monday night, with the highest river flows expected on North and West Vancouver Island, Metro Vancouver's North Shore and the Lower Fraser Valley.

"Uncertainty remains high about the specific storm track and rainfall amounts, as well as the significance of rain-on-snow inputs," reads the centre's advisory. "If temperatures are slightly warmer than forecast, snowmelt and rain-on-snow may provide substantial additional contributions to runoff."

B.C. Ferries said Monday afternoon it has cancelled several Christmas Day sailings on multiple routes and many more were at risk as the storm made landfall.

The ferry corporation says it cancelled afternoon sailings on routes serving Alert Bay, Powell River and Comox, in the South Coast, due to the weather. It also cancelled the 7 p.m. and 9 p.m. sailings between Tsawwassen and Swartz Bay.

B.C. Ferries says on its website that the safety of its crews and passengers are "of primary importance" and it is apologizing for any inconvenience the cancellations may cause over the holidays.

An atmospheric river is a term used to describe large streams of water vapour that can bring heavy amounts of rain and precipitation, particularly in mountainous areas like the South Coast.