Monday, August 23, 2010

Warm Water in the Cool Northwest

Want to swim in relatively warm water while staying in the Northwest?

Hit the surf while avoiding that expensive trip to Hawaii?

Its possible. Just like our weather features, local water temperatures also have some interesting variations.

For example, check out the average sea surface temperatures (SSTs) for the last three days for our area:

The warmest temperatures...in the mid 60s!...are found in the inland waters between Vancouver Island and the mainland. Along the Pacific coast the coolest water temperatures are right near the coast, and temperatures warm considerable (into the 60s!) offshore. So cancel that trip to Hawaii...warm water is just a short boat ride away.
Here is a view father down the coast...again, cool water right along the shore and warmer water offshore. You got to go south of Santa Barbara before the coastal sea surface temps become swimable.


So what is going on? A conspiracy against swimming on the Pacific beaches? And why are the inland BC waters so warm?

The reason behind the cool coastal temps is well known...upwelling. During the summer northerly winds dominate along the west coast as the east Pacific anticyclone (high pressure area) strengthens. These winds put a force on the water towards the south. But something else is going on. The turning of the earth produces a Coriolis Force to the right of motion, which in this case creates an offshore (westerly) component to the surface water. Well, if water is moving away from the surface near the coast, some other water has to take its place...water from below. This water is cooler than the surface waters and thus this upward motion (upwelling) causes cooling within tens of km of the coastline. (see my book for a more detailed explanation). The offshore warm water is why many fisherman head west to catch warm-water species (like albacore tuna).

Loads of tuna offshore of the Washington Coast.
Picture courtesy of Ocean Charters in Westport

Coastal BC waters have limited input from the Pacific, are relatively shallow, and get fed by a number rivers, whose waters are relatively warm. That is why many BC people don't feel the need to go to Hawaii. I have been to Hawaii a few times and have never met anyone from BC there, which proves my point.

Relatively warm water is found in some of the large Puget Sound lakes. Take Lake Washington. After a warmer summer period the surface temperature can get into the low 70s. But beware, very cold water is below. Want to see proof? Here are some vertical distributions of temperature (black line) and other parameters from a buoy on Lake Washington. Warm near the surface (20C is 68F) , but head down more than 10 meters (roughly 30 ft) and it gets very cold, very fast.


Of course, high mountain lakes (like Lake Diablo in the N. Cascades) can be much cooler, some in the 40sF. Not good for swimming.

So I hope I have convinced all of you that there is no need to go to Hawaii to enjoy temperate waters. You can send me all the airline tickets to that destination that you won't be using.

4 comments:

Dan McShane said...

Dabob Bay or Quilcene Bay for me. Its closer than the coast

davidb said...

I believe Kopachuck State Park has water temperatures in the mid to upper 70s by late summer. I know I was astounded by how warm the water was when I swam there a decade ago.

Apparently it's due to the water passing over sun-warmed tidal flats on its way in.

JewelyaZ said...

I'll stick to the Bellevue Aquatics Center, thanks! The big pool there is 86F and the therapy pool is 91F (aaaaaaaah!) All this can be yours for 3 hours for $4.25... much cheaper than the gas to go to the coast!

I grew up in North Carolina and don't consider ANY of the natural outdoor water here "swimmable". Beautiful, scenic, critical for the animals -- all of that, yes, but not for swimming.

Ocean temps in the Atlantic are much warmer in the summer, and the Gulf of Mexico off western Florida feels like a bathtub... also more my speed when there's no oil in it.

John Davidson said...

We go north to Desolation Sound in our boat and swim in the warm water every day. Pendrell Sound is the warmest water north of Mexico on the West coast, usually around 75-80F during the summer.