Winds, Tides, and Weather


Bill Trandum

Puget Sound Winter Sailing

One thing a Puget Sound sailor can be sure of, if the wind from October to May is not from the south or southwest, it soon will be.

Relatively warmer ocean water spots, perhaps caused by undersea volcanic activity in the Gulf of Alaska, cause the air molecules over them to rise, leaving areas of low atmospheric pressure behind. As the Earth turns from east to west under that low-pressure area, the low-pressure cell moves from west to east, all the while sucking air, generally from the south, to fill the void left behind.

The resulting low-pressure cell slips southward because of the less dense atmosphere of warmer air molecules there. The Earth's rotation causes the low-pressure cell to park over Vancouver Island, aided by the Vancouver Island coastal mountain range that forces the air upward, and then by the Canadian Rockies that do the same thing.

As the stalled low-pressure system sits there, more southerly air molecules, often saturated with moisture from the Hawai’ian “ Pineapple Express,” rush in to give the Pacific Northwest its rainy south or southwesterly winds and weather.

Sometimes it rushes in great gulps, as I learned in Seattle's Elliot Bay one February, complete with what's called a spinnaker knockdown. We were racing along in a 40-foot sailboat when a blast of wind hit us. The boat lay over on her side; all sails in the chilly water and one man overboard (thankfully not me, but I was the guy who got his fingers through the lacing on his life jacket and hung on until the other crew members hauled him back aboard). As soon as we were upright, we continued racing and finished third, with a great story to tell.

Every once in a while in the dead of winter, a huge polar air mass will move from Siberia across Alaska and Canada, bringing frigid temperatures south. Where that icy air mass meets up with the warmer water-saturated air molecules from the Southwest Pacific, winter snow is the result. That may cause trouble in the lowlands, but it’s a gift to the higher elevation ski resorts. Come spring, the snow melt runoff fills the rivers and streams, sending their signature tastes and scents so the salmon know where to go to deposit the next generation of fry, and to provide enough stream flow for the fish to get there.

Tidal flows also play a big role in Puget Sound, the rule being that the ebbing or flowing current is weakest along the shore and strongest out in the middle of the Sound. And as the tide changes from ebb to flow or the reverse, it starts along the shore, and then moves off the beach into deeper water.

A big exception is the west side of Vashon Island. There, in Colvos Passage, the current always flows north regardless of the stage of the tide, an anomaly caused by the configuration of the sea bottom in that channel.

For the Puget Sound sailor, being able to predict and read the wind direction is a real gift. Knowing that in the winter a northerly wind is rare and an easterly wind even rarer, he or she wisely heads the boat in a direction that will economically use the airflow across or against the sails to get where he or she wants to go.

Bill Trandum, a retired U.S. Navy captain and self-described student of all things wind, waves and weather, lives in Vaughn.