Sea surface height anomalies on September 3, 2006, during a weak El Niņo event. Yellow and red areas indicate where the waters are relatively higher (warmer) and have expanded above.

NASA satellite data indicates El Niņo has returned to the tropical Pacific Ocean, although in a relatively weak condition that may not persist and is currently much less intense than the last major El Niņo episode in 1997-1998.

Over the past several weeks, NASA's Aqua and Jason satellites have observed a general warming of ocean temperatures and a rise in sea surface heights in the central and eastern Pacific along the equator, both indicators of El Niņo development.

"The present conditions indicate that the intensity of this El Niņo is too weak to have a major influence on current weather patterns," said Bill Patzert, oceanographer and climatologist at the NASA's Jet Propulsion Laboratory, Pasadena, Calif. "But, if the ocean waters continue to warm and spread eastward, this event would likely strengthen, perhaps bringing much-needed rainfall to the southwestern and southeastern United States this winter."

The National Oceanic and Atmospheric Administration, the lead U.S. agency on monitoring and forecasting these events, has also recently noted other signs of a developing El Niņo, including below-normal rainfall in Indonesia, Malaysia and the Philippines. These areas are usually the first to respond to an El Niņo pattern as trade winds relax due to higher-than-normal air pressure in the region.

Still, scientists remain doubtful about whether the observed El Niņo will persist. They say it is important to wait and see how ocean conditions evolve over the next couple of months since there are natural fluctuations that result in a short-term tendency toward warmer water on the Pacific equator at this time of year.

According to researchers, the current El Niņo signal is far less dramatic than that seen during the start of the last major El Niņo episode in 1997-1998. That event brought devastating floods to California that cost millions of dollars in damage while severe drought struck Indonesia, Australia and the Philippines.

El Niņo is a cyclical warming of the ocean waters in the central and eastern tropical Pacific that generally occurs every 3 to 7 years. It is associated with changes in air pressure and the movement of high-level winds that can affect weather worldwide. Typically peaking during the winter months, El Niņo is the warm phase of the El Niņo/Southern Oscillation. It alternates with La Niņa, the cooling of ocean waters in the same region of the Pacific.

In the United States, El Niņo normally results in warmer-than-normal temperatures across the northern and western states. Wetter conditions often prevail over much of the south with dry weather across the Ohio Valley and Pacific Northwest.

During the next several weeks and months, scientists at the National Oceanic and Atmospheric Administration and NASA will continue to closely monitor conditions in the Pacific to determine how the evolution of this El Niņo may impact weather patterns this winter.

For more information and related images, visit on the Web:

http://www.nasa.gov/vision/earth/lookingatearth/elnino_return.html