Signs are getting stronger that an El Niño will affect the world’s climate during the rest of 2015. El Ninos occur when trade winds slacken across the equatorial Pacific. This allows warm water that has piled up in the western Pacific to move eastward in what oceanographers term a “Kelvin Wave.’ The figure above, jointly produced by the International Research Institute for Climate and Society and the Climate Prediction Center, shows results from model forecasts of sea surface temperature produced by organizations around the world. Anything above zero indicates warming in the in the Niño 3.4 area (the region 5 degrees north and south and the equator between 120° and 170° west longitude) with the larger the number corresponding to a greater warming and stronger El Niño.
The greatest warming is forecast by the United States Climate Forecast System version 2 model, or CFSv2, with a temperature anomaly greater than two Celsius degrees seen in the northern hemisphere fall of this year, with longer ranger models showing a large anomaly persisting at a high level into the winter.
Strong El Niños are often characterized by heavy rains in Southern California and the southern tier of states. It is possible that we are already seeing El Niño type storms affecting Southern California, at a time of year that is typically dry. Although just about halfway through the month, this is already the second rainiest May on record in San Diego. Much of that rain fell during flash flooding on May 14, when about one and half inches of rain fell in 90 minutes and 0.71 inches in just 9 minutes! Such an intense downpour only occurs in San Diego on average every one to two centuries. While El Niño may bring heavy rain and flooding to the southern parts of California, that does not necessarily mean that the northern watersheds that supply so of California’s precious water will be filled, northern California precipitation can be hit or miss during El Niño years.