El Nino, La Nina

Pacific La Nina Building?

By Joshua S. Hill

Sunday, September 9, 2007

Scientists with NOAA's Climate Prediction Center in the release of its latest monthly El Nino/Southern Oscillation (ENSO) Diagnostic Discussion are predicting that another La Nina event is on its way.

"While we can't officially call it a La Nina yet, we expect that this pattern will continue to develop during the next three months, meeting the NOAA definition for a La Nina event later this year," said Mike Halpert, acting deputy director of the Climate Prediction Center in Camp Springs, Md.

A La Nina event is characterized by unusually cold ocean temperatures in the eastern equatorial Pacific, compared to the El Ninos effect which sees the reverse happen in the same area. In the most recent ENSO Diagnostic Discussion, released on September 6, they note that during August 2007 "negative sea surface temperature (SST) anomalies in the eastern equatorial Pacific expanded westward, and now extend from the coast of South America to the date line (180ºW)".

The last major La Nina event occurred back in 1988/89, followed ten years later by a moderate event, that concluded in Fall (Autumn) of 2000, which was ostensibly the last La Nina event to have occurred. In the intervening years, there have been two El Ninos event

According to Halpert, nearly all the operational dynamic and statistical models focusing on this effect, including the National Centers for Environmental Prediction's Climate Forecast System, believe that a La Nina will be announced later this year.

If La Nina is announced, seasonal forecasters believe that wetter than average conditions will occur in the Pacific Northwest of America, and even drier conditions will be expected in the already drought stricken southwestern United States this coming Fall (Autumn).

"These conditions also reinforce NOAA's August forecast for an above normal Atlantic hurricane season," said Gerry Bell, Ph.D., NOAA's lead seasonal hurricane forecaster. Already there have been five named-Atlantic storms and two hurricanes. Hurricanes Dean and Felix both broke previous recorded records by reaching Category 5 wind-speeds before touching land.

The most recent, Felix, slammed in to Nicaragua on Tuesday with catastrophic 160 mph sustained winds and a storm surge estimated at 18 feet above normal tides. Already rescue workers have raised the death toll to 40, and announced that dozens more are still unaccounted for.

Hurricane forecaster William Gray, at Colorado State University downgraded his predictions slightly this past week, revising it down to only five more hurricanes, two of which would be major storms with sustained wind-speeds in excess of 111mph. He had originally predicted a 2007 hurricane season well above average, and while his revised estimate is still above the norm, it is not as extreme as originally thought.

La Nina and El Ninos are, as mentioned, opposite sides of the same coin, and act as randomly and unpredictably as a coin toss. Both are unpredictable in the long term, and do not follow any regular trends.