National Weather Service Weather Forecast Office

Dec. 7, 2006 — The latest El Niño/Southern Oscillation Diagnostic Discussion, produced by scientists at the NOAA Climate Prediction Center, indicates El Niño conditions are now evident in the tropical Pacific and should intensify during the next one to three months. However, this episode is expected to be much weaker than the very strong 1997-1998 El Niño event. (Click NOAA image for larger view of winter outlook for December 2006 through February 2007, including the position of the jetstream and what this moderate El Niño event is expected to produce. Click here for high resolution version. Please credit “NOAA.”)

“Evolving current conditions in the equatorial Pacific are likely to cause a substantial increase in sea surface temperature along the west coast of South America in late December 2006 and January 2007,” said Vernon Kousky, Ph.D., NOAA’s lead El Niño forecaster. “At about the same time, rainfall is expected to increase over the warm waters in the central equatorial Pacific, thus setting the stage for typical El Niño effects over the U.S. during January through March 2007,” he added.

El Niño events influence the predominate position and strength of the jet stream over the Pacific Ocean, which in turn affect winter precipitation and temperature patterns across the country. During El Niño events, the jet stream is stronger than normal across the southern U.S. As a result, increased storminess and wetter-than-average conditions occur across the southern tier of the U.S. from central and southern California across the Southwest to Texas and across the Gulf Coast to Florida and the Southeast. Meanwhile, drier-than-average conditions are experienced in the Ohio and Tennessee Valleys, and in the northern Rockies. (Click NOAA satellite image for larger view of sea surface temperature anomalies as of Dec. 5, 2006. Click here for high resolution version. Please credit “NOAA.”)

“NOAA’s investment in climate models is paying off,” said Jim Laver, director of the NOAA Climate Prediction Center. Statistical and coupled model forecasts, including the NOAA National Centers for Environmental Prediction Climate Forecast System, show El Niño conditions peaking during the northern hemisphere winter (December 2006 through February 2007) and then weakening during the northern hemisphere spring (March through May 2007). “This event may be with us for a while, and we will be closely monitoring how the atmosphere reacts,” he said.

The term El Niño refers to the large-scale ocean-atmosphere climate phenomenon linked to a periodic warming in sea surface temperatures across the central and east-central equatorial Pacific (between approximately the date line and the South America coast). El Niño represents the warm phase of the El Niño/Southern Oscillation, or ENSO, cycle, and is sometimes referred to as a Pacific warm episode. Originally, the term referred to an annual warming of sea surface temperatures along the west coast of tropical South America. Typically, El Niño episodes occur every 3 to 5 years. However, in the historical record this interval has varied from 2 to 7 years.

The next El Niño/Southern Oscillation Diagnostic Discussion will be published (via the Internet) on January 11, 2007.