El Niño is back

On September 10 the US National Oceanographic & Atmospheric Administration (NOAA) declared that El Niño is back but this time around in a weaker state. "El Niño conditions have developed in the tropical Pacific and are expected to last through early 2005," said Jim Laver, director of the NOAA Climate Prediction Center. "At this time it is not clear what, if any, impacts this event will have on ocean temperatures in the classical El Niño region along the west coast of South America and on temperature and precipitation in the United States."

Impacts depend on a variety of factors, such as the intensity and extent of the warming in the tropical Pacific. NOAA will continue to monitor the situation in the tropical Pacific and will provide more detailed information on possible impacts due to this event in coming months.

In the release of the El Niño Diagnostic Discussion, the NOAA Climate Prediction Center scientists noted that sea surface temperatures (SSTs) were more than 0.5 degrees C above average in the central and western equatorial Pacific during August 2004. By early September, positive SST departures greater than 0.5° C (~1° F) were found between 160E and 120W, with departures greater than 1° C extending from 170E eastward to 140W.

"The increase and eastward expansion of warmth in the central equatorial Pacific during July through August indicate the early stages of a warm (El Niño) episode," said Vernon Kousky, NOAA's lead ENSO forecaster. He added, "Through the end of August conditions were not yet indicative of a basin-wide El Niño, particularly due to the presence of below normal sea-surface temperatures in the far eastern equatorial Pacific near the South American coast." The lack of basin-wide warming indicates that this El Niño is likely to be much weaker than the 1997-1998 event.

NOAA declares the onset of El Niño conditions when the three-month average sea-surface temperature departure exceeds 0.5° C in the east-central equatorial Pacific [between 5° - 5° S and 170° W - 120° W]. To be classified as a full-fledged El Niño episode, these conditions must be satisfied for a period of at least five consecutive three-month seasons.

El Niño is associated with changes in sea surface temperatures in the tropical Pacific Ocean and can have significant impacts on weather around the world. El Niño episodes occur about every four to five years and can last up to 12 to 18 months.

The El Nino/Southern Oscillation (ENSO) Diagnostic Discussion is a consolidated effort of NOAA and its funded institutions. NOAA will continue monitoring El Niño developments and provide monthly updates through its El Niño/Southern Oscillation (ENSO) Diagnostic Discussion. The next update will be issued on October 7, 2004, in association with the US Winter Outlook.

NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nationís coastal and marine resources. NOAA is part of the US Department of Commerce.

For more information go to the NOAA website at http://www.noaanews.noaa.gov/stories2004/s2317.htm

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