It is not unusual during summer to view a satellite image like the following, with a narrow sliver of low cloud along the Northwest coast. Why does this occur?
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| MODIS satellite image on August 12th |
The answer: cold water along the coast due to ocean upwelling (cold water coming up from below). It is not usual during the summer to have coastal water temperatures 10F or more cooler e than what we observe 0-15 miles offshore.
Let me give you some recent examples. Here is the latest National Weather Service sea surface temperature (SST) analysis for today...notice the cold temperatures from San Luis Obispo on the southern CA coast to our area, with the coldest temps along the northern CA coast.
We can take a closer look off the Oregon coast by viewing the SSTs forecast by the Oregon ROM ocean modeling system (I used the
NANOOS web site to plot this). Lower to mid-50s along the coast while lower 60s are waiting 100 miles offshore.
Or take a look at the last NOAA SST analysis for the NW coast. A veneer of cold water follows the coast.
Buoy 27 is found right off the Oregon/CA border and temperatures there have been dropping into the lower 50s.
But head out to Buoy 46006 and temperatures in the in sultry mid to upper 60s.
The offshore water is warm enough for albacore tuna, so a number of Washington and Oregon fishing charter companies head offshore 10-30 miles to give anglers a chance to bring in some tuna.
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| Image courtesy of Deep Sea Charters, Inc. of Westport |
Coastal cold water is typically a warm-season coastal ocean feature around here. This is because the East Pacific High moves northward during the summer, producing northerly winds along the coast. These northerly wind push the coastal water southward, but the Coriolis force then acts on the moving water, giving it a torque to the right (offshore). Move surface water offshore and water comes up from below to take its place (see figure).
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