El Niño August update - Tucson News Now

El Niño August update

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El Niño is still in the forecast to develop this year, but the latest computer models show a weaker event than in previous runs. The Climate Prediction Center (CPC), which tracks El Niño development, released the latest forecast discussion on August 7, 2014. According to the CPC, "over the last month, model forecasts have slightly delayed the El Niño onset, with most models now indicating the onset during July-September, with the event continuing into early 2015.: 


This could still be good news for Arizona.  When El Niño coincides with winter months, Arizona generally has a wetter than average winter. The winter storm track drops farther south than average allowing storms to dump more rain and snow on the state than is typical of an Arizona winter.


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 is when the SSTs are warmer than average versus La Niña, which is when SSTs are cooler than average. The below image from National Climate Data Center shows how El Niño influences weather during the cool and warm months in the Northern Hemisphere.   



The below image shows the latest El Niño forecast from the CPC. The '0.0' line indicates average SST. The colored lines represent different computer models that forecast El Niño and La Niña trends. The thicker yellow line is the average of all the model data.  The letters at the bottom represent the months. For example, 'JJA' represents June, July, and August. In the forecast, you can see that the yellow line is trending slowly upward through the rest of summer and into fall. Once the line goes above '0.5', an El Niño is in the forecast. The current observations show the SSTs are hovering around this threshold.  


Earlier this year the developing El Niño looked similar to the start of the strong 1997/1998 event. However the numbers have since backed off and the CPC says "a strong El Niño is not favored in any of the ensemble averages, and slightly more models call for a weak event rather than a moderate event." However the "chance of El Niño has decreased to about 65% during the Northern Hemisphere fall and early winter" according to the CPC. 

The below image is from Columbia University. The red bars show an increasing confidence that an El Niño will appear as we head through the rest of 2014.  

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