Tag Archives: West Coast

Sea Surface Temperatures: West Versus East Coast.

From The Cliff Mass Weather Blog

By Cliff Mass

Perhaps, this blog spends too much time talking about the atmosphere, so to make amends today, let’s see what is happening to the temperature of the ocean surface.  And see whether anything unusual is going on. Let’s start with yesterday’s sea surface temperatures around North America (below).  Sorry, it is all in °C.   Keep in mind that 10°C is roughly 50F,  20°C is around 68F, and 30°C is approximately 86F.

The eastern Pacific near the West Coast is cold (about 50F), with central California’s waters a bit cooler than ours. You must head to the southern tip of the Baja Peninsula to find the water warm enough for comfortable swimming.

The East Coast is a study in contrasts.  The water off of New England is crazy cold (dropping below 7C), while the uber-warm Gulf Stream is found along the west coast of Florida, moves past the Carolinas, and then heads northeastward into the Atlantic.    

There is a HUGE temperate contrast between the Gulf Stream current and the cold water of the Northeast.    A blow-up of the sea surface temperatures off the Northwest really shows the amazing horizontal temperature changes north of the Gulf Stream

Look closely and you will waves in the interface between warm and cold water in the Atlantic and a fascinating loop in the warm water over the Gulf of Mexico (first image above).    Very warm water over the Caribbean and west of Central America

Your next question is probably:  is the current pattern of sea surface temperature unusual?  

To evaluate this, the next map shows the difference between yesterday’s sea surface temperature and normal conditions (also called the SST anomaly).

Pretty close to normal off the Northwest coast.  A few degrees colder than normal for California’s coastal waters. And near normal on Mexico’s west coast.   Most of the Gulf and Atlantic coast is slightly above normal. Temperature is cooler than normal north of the Gulf Stream, which suggests that the Gulf Stream is south of its normal position by a hundred miles or so.

The biggest sea surface temperature story is what is happening in the tropical Pacific.  Last year, a strong El Nino brought MUCH warmer than normal sea surface temperatures from South America, westward into the central Pacific.  

But something major has happened.  The tropical Pacific surface waters are rapidly cooling, resulting in cooler than normal waters in many locations (see map, with arrows showing you some of the coolest spots).

El Nino is dead.  Long live La Nina, its frigid cousin!

Why does El Nino Influence West Coast Weather?

From The Mass Weather Blog

Cliff Mass

As I have noted in a recent blog, it is no surprise that the low snowpack and warm temperatures have occurred over the Northwest during the past month or so.

This is a very typical pattern during El Nino years.

In particular, during El Nino years, when the tropical Pacific is warmer than normal, we often experience low pressure off the West Coast, with storms shunted into California.

To illustrate the current situation, here is the difference from normal of sea level pressure for the past two months.  You can see the anomalous low pressure to our southwest.

This pattern pushes the jet stream south and leaves California wetter than normal.  But their boom is our bust.

But why does El Nino set up this pattern?

Why do warm sea surface temperatures in the tropical Pacific associated with El Nino alter the pressure and wind patterns off the West Coast.

The answer to this question was found in the late 1970s and early 1980s by two researchers at the UW:  graduate student John Horel and Professor Mike Wallace.

First, the warm waters of El Nino (illustrated by the shaded area near the equator) perturb the atmosphere above.  

How?  By creating lots of thunderstorms over the warm water.  Thunderstorms that inject huge amounts of energy into the atmosphere (see below).

A series of waves….called Rossby Waves…then propagate into the midlatitudes, causing a series of low and high-pressure pressure areas (note the L’s and H’s in the figure in the figure below). 

 The jet stream….the current of strong winds in the upper troposphere… is distorted by this wave pattern (see the arrows in the figure).  This pattern is generally associated with low pressure off the northern CA coast.

This situation is analogous to throwing a rock into a stream, with waves propagating away from where the rock hits the water.  

In the atmospheric case,  big thunderstorms above the warm water act as the “rock,”

During the next few months as El Nino makes way for La Nina, the central Pacific water will cool, the thunderstorms will shift westward, and the wave pattern change substantially.