Latest forecast shows possible strong El Niño, good/bad for AZ - Tucson News Now

Latest forecast shows possible strong El Niño, good & bad for AZ

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It appears a strong El Niño is in the making and that means good and bad news for Arizona. 

El Niño and La Niña refer to the sea surface temperature (SST) of the eastern equatorial Pacific Ocean, off the coast of central America.  The temperature of the water in this area can influence weather across the world, including right here in Arizona.

El Niño shows the strongest link between SSTs and weather in Arizona.  El Niño is when the SSTs are warmer than average.  When El Niño coincides with the winter months, Arizona generally has a wetter than average winter. 

During the monsoon, El Niño tends to push towards a drier summer.  Some evidence shows the ideal atmospheric set-up for the monsoon is weakened during El Niño events.  

However, warmer than average SSTs during El Niño mean there is more energy available for tropical storms and hurricanes to form in the East Pacific.  If these storms track along or hit the west coast of Mexico, surges of tropical moisture can ramp up monsoon storms and have historically caused major flood events for parts of Arizona.  

The monsoon-El Niño link is currently a weak area of research and scientists continue to explore the data.  

The latest El Niño forecast from the Climate Prediction Center (CPC), a division of the National Atmospheric and Oceanic Administration, was released this morning.  The CPC says changes in the ocean in the last few months produced a spike in ocean heat content making it the "largest March value in the historical record back to 1979".  The image below shows that spike mostly happening in February and March of this year.  

The spike indicates a strong El Niño could be forming by summer.  

The movie below shows the progression of the ocean heat content since the start of 2014. 

The left-hand numbers show the depth of the Pacific Ocean at the Equator.  The numbers at the bottom show the longitude of the stretching from the western Pacific, just north of Australia and the eastern Pacific, near the west coast of South and Central America.  The colors show how warm the ocean water is compared to average. The brighter colors indicate a pool of warm water.

Since the start of 2014 a warm pool of water has been growing below the surface of the ocean, moving east, and floating upward near the Equator of the Pacific, as seen in the progression of the reds, yellows, and oranges in the animation.  Once that water reaches the surface an El Niño becomes reality.  

The below image shows the latest El Niño forecast from the CPC. The '0.0' line indicates average SST.  All the lines represent different computer models that forecast El Niño and La Niña.  The thicker yellow line is the average of all the model data.  The letters at the bottom represent the months.  For example, 'FMA' represents February, March, and April. 

In the forecast, you can see that the yellow line is trending upward through spring but the line stays below '0.5', which is the cutoff for El Niño.  However, heading into summer (JJA - June, July, August) the yellow line exceeds that threshold, indicating an El Niño will form.  

The CPC is still cautious of the forecast saying "Despite this greater model consensus, there remains considerable uncertainty as to when El Niño will develop and how strong it may become. This uncertainty is amplified by the inherently lower forecast skill of the models for forecasts made in the spring."

However the agreement among the models shows a greater than 60 percent chance an El Niño will form late summer or fall of this year.  The below image is from Columbia University.   The red bars show an increasing confidence that an El Niño will appear by at least the end of the year.  

This means a cool, wet winter may be in the forecast of Arizona. 

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