El Niño is coming

In a bulletin issued this morning, NOAA issued an El Niño Watch predicting a roughly 50 percent chance for development later this year. An “El Niño” is the abnormal warming of ocean temperatures in the eastern Pacific Ocean along the west coast of South America near Peru and Ecuador. It can have profound influences on weather patterns around the world.

NOAA’s bulletin says “sea surface temperature anomalies have recently increased near the International Date Line” as well as “in the central and east-central equatorial Pacific,” and that “many dynamical models predict El Niño to develop during the summer or fall.”

El Niño conditions are declared when the average sea surface temperatures in the eastern Pacific are at least 0.5°C above average for three consecutive months. These abnormally elevated sea surface temperatures allow for the atmosphere to warm and provide instability, leading to the development of thunderstorm activity.

The warmer temperatures caused by an El Niño tend to alter the jet stream in the Northern Hemisphere, allowing a subtropical jet stream to form north of Hawaii and extend across parts of the western and southern United States. Increased thunderstorm activity over the eastern Pacific allows moisture to rise into the upper atmosphere and leak into this branch of the jet stream, creating the opportunity for beneficial rainfall across the affected areas next fall and winter, especially in California where they are experiencing exceptional drought conditions.

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