All About El Nino - A
April 9, 2012

All About El Nino Meteorologist Joshua Kelly

El Nino is a term used to describe a weather pattern that sets up in the Tropical Pacific Ocean. So you may ask why does it matter to me and should it matter to me? The answer is yes because it impacts each and every one of us on Earth. The impacts are felt from weather pattern changes to lifestyle changes. As we know, off the coast of Peru normally they will have cold upwelling waters that are found off the coast. This is important because it supports their fishing industry. Now, during an El Nino period this water warms up which impacts the fishing industry along their coast.

So to understand what El Nino is we first must understand what is considered a normal Pacific Ocean circulation pattern.

Normal Pacific Ocean:

The image above shows us what is considered normal in the Pacific Ocean. That is cold waters off the coast of Peru and also the West Coast of the United States are heading westward towards the other side of the Pacific Ocean. At the same time you can see the warm waters from the Western Pacific are headed eastward towards the West Coast of the United States. This is a general flow during normal conditions.  So now the next thing we have to think of is how a bathtub works and that is when the water is moved back and forth it causes one side of the tub to be higher for a time period as the waves of the tub move back and forth. This is the same thing that happens in the Pacific Ocean as the Western Pacific is a tad bit deeper than the Eastern Pacific. This is important to know because just like a bath tub over a period of time it works and forces the warm waters to head over towards the Eastern Pacific in great amounts more than normal. To understand how that works it is important to understand our next feature which is trade-winds.

Pacific Ocean Trade Winds:

In this diagram above we see what is called a wind barb. A wind barb helps meteorologists determine wind speeds and directions. Also the on the wind barb you will see each diagonal line which represents speed of the winds. One full barb would be 10kts of wind. In this example we have two, meaning our winds are 20kts. This is normally what occurs in the Pacific Ocean -- strong winds off the coast of Peru pushing cold water westward at fast speeds. As the water travels westward it gets warmer as it moves across the Pacific. So this is what we expect to see in the Pacific during normal conditions.

Now let´s look at how things change during El Nino periods. First, it is important to understand that El Nino occurs in cycles happening every 3-7 years with the average being around 5 years.  Once El Nino begins it usually takes up to 9 months to run its complete cycle.  So the first diagram below we can see what happens with the water circulation during El Nino.

EL NINO Conditions:

Now we see that the warm waters from the Western Pacific are headed back towards the Eastern Pacific and also we are now dealing with warm waters around Peru unable to transport the colder waters westward. How does this happen? To answer this we have to look at our trade-winds. As you remember during normal conditions, the winds were around 20kts, however during El Nino the winds become weaker in the Eastern Pacific which does not allow the water to move westward as fast and it actually starts to reverse just like the bathtub effect.

EL NINO Trade-winds:

Now we notice that are winds have decreased to only around 5-10kts. This is huge because we have all this extra water that is usually pushed across the Pacific with winds around 20kts now the winds have been cut in half at best. This leaves all this extra water to start piling up along the Eastern Pacific now.


Above we see some of the conditions that occur during El Nino. First, over in the Western Pacific around Australia and Indonesia we see warm and drier conditions which can lead to periods of drought because of the decrease in precipitation during this time period.  Secondly we see that our frontal boundaries tend to shift further southward in the United States which mean that heavier rainfall and stormy weather pattern tend to impact the Southern part of the United States more frequently. The third area of concern is along Peru where we see two major impacts the first being the sea surface temperatures increasing this is a huge impact because it impacts the fishing waters off the coast. Secondly this warmer water leads to an increase in moisture for the Peru dry-lands causing flooding and extensive damage to the area. And another large impact of El Nino is probably a good thing for the United States and that is we usually see a decrease in Tropical Weather in the Atlantic Ocean.

These are only some of the impacts that El Nino brings but as we can see this is a huge global shift in weather which leads to large impacts on many people from drought to heavier than normal rains.

So the burning question is now when can we expect to see the next El Nino if we look back the last El Nino was documented as occurring back in 2010 so if we look at the information available we could be coming around the corner to another El Nino period soon.

Indications are pointing towards the possibility of El Nino setting up later this summer early into this winter, however until it happens we just got to sit back and wait. Now that you see what some of the impacts are in regards to El Nino you can be better prepared for this event.  So we have seen that there is a Normal condition in the Pacific Ocean and also El Nino so is there a reverse to El Nino and the answer to that is La-Nina.