Our Washington Coastal Water Temperatures are Warmer Than Normal. Why?

 The latest NOAA map of coastal water temperatures along the southern Washington coast shows temperatures above 61F (16C)...see below.  Cooler water is found along the Oregon and California coasts.  Much warmer water is found offshore.  At Ocean Shores or Long Beach, you could almost go into the water without a wetsuit.

How do these temperatures compare to normal?  Below are the anomalies (differences) from climatology (or normal conditions) of the sea surface temperatures. Warmer than normal by 2-3C along the coast and the warmth extends offshore. Cooler than normal along the California coast.



Before I explain why, I wanted to mention that late August is the time of typically warmest temperatures along our coast.  To illustrate, here is a plot of climatological sea surface temperatures at Ocean Shores, WA from the excellent website, Weatherspark.  The typical highest ocean temperature is on August 28th at 58F, compared to the lower 60s today.


So why are water temperatures warmer than normal this year?   A key issue is that the upwelling of cold water from below the surface is weaker.

And why is it weaker?  Because the normal high pressure offshore has been weaker than normal during the past months.  

High pressure offshore results in northerly winds (winds from the north) along our coastal zone. These winds blow on the ocean surface, and because of the rotation of the planet, this results in water currents being directed offshore.  To make up for the lost water, cool water comes up from below.

 The latest NOAA map of coastal water temperatures along the southern Washington coast sho Our Washington Coastal Water Temperatures are Warmer Than Normal. Why?

High pressure offshore....known as the East Pacific High-- is associated with northerly winds along the coast (see schematic).

 The latest NOAA map of coastal water temperatures along the southern Washington coast sho Our Washington Coastal Water Temperatures are Warmer Than Normal. Why?

During the past month, an unusual area of low pressure was positioned off the Oregon coast, something shown by the difference in pressure from normal for the past 30 days found below.  This resulted in weakened northerly winds, less upwelling of cooling water from below, and warmer than normal coastal temperatures.  

Now you know.

Sea level pressure difference from normal during the past month



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