Pineapple Express rushes in

No-one on Gabriola will have failed to notice that it's hardly stopped raining in the past week - and that temperatures have been unseasonably high.

At midnight last night, the temperature here on Gabriola was hovering around 12C - nearly 10 degrees warmer than normal for this time of year.  On Monday, Vancouver International Airport registered a record high temperature of 13.1 degrees. The previous record of 12.2 degrees was set back in 1941. The mild temperatures will continue for the next few days although no records are expected to be broken.

After a brief respite this morning, the rain is back and is expected to continue on and off  for the next week.

The cause of this unusual phenomenon?  The so-called Pineapple Express - a strong and persistent flow of atmospheric moisture and associated heavy rainfall from the waters adjacent to the Hawaiian Islands and extending along the Pacific coast of North America.

A Pineapple Express is driven by a strong, southern branch of the Polar jetstream and is usually marked by the presence of a surface frontal boundary which is either slow or completely stationary, with waves of low pressure traveling along its axis. Each of these low pressure systems brings enhanced rainfall.

The conditions are often created by the Madden-Julian oscillation, an equatorial rainfall pattern which feeds its moisture into this pattern. The composition of moisture-laden air, atmospheric dynamics, and orographic enhancement resulting from the passage of this air over the mountain ranges of the western coast of North America causes some of the most torrential rains to occur in the region. In British Columbia, Pineapple Express systems typically generate heavy snowfall in the mountains and Interior Plateau, which often melts rapidly because of the warming effect of the system.

Throughout Vancouver Island, the effects of this Pineapple Express are already being felt.  

The mayor of Courtenay, B.C. has declared a local state of emergency after heavy rain caused local rivers to flood their banks, forcing the evacuation of about 40 people in the city on the east coast of Vancouver Island. Mayor Greg Phelps issued the order after high water levels in the Browns, Tsolum and Puntledge Rivers caused flooding in the low lying areas adjacent to the Tsolum River and Courtenay River overnight Monday.The city also opened a local community centre for any evacuated residents, closed several roads and the Fifth Street bridge, and urged drivers to avoid the city's downtown core.

B.C.'s River Forecast Centre has also posted flood warnings for the nearby Puntledge and Browns Rivers while a flood watch is in effect along the Nanaimo River, south of Nanaimo.

The mayor plans to keep the state of emergency in effect for several days because there are very high tides forecast through the week and more heavy rain in the forecast. "We've decided to keep our local state of emergency in effect, because that gives us the power to keep things like the reception centre and the people in the emergency shelters," said Phelps.

Residents in low-lying areas of Courtenay were evacuated in mid-November when heavy rains, melting snow and high tides pushed the Puntledge, Courtenay, Tsolum and Browns Rivers over their banks. Further south on the island, residents of Duncan and Cowichan were also evacuated last November, but so far this week, that area has not been affected by flooding.