ENSO - El Niño / La Nina Information for Site 171

ENSO (El Niño Southern Oscillation) is the warming and cooling of the ocean water along the Equator in the Eastern Pacific Ocean near South America. The warm phase is called El Niño and the cold phase is called La Nina.

When the Eastern Pacific Ocean is 0.5 degrees Celsius above normal for 5 consecutive 3-month average periods, an El Niño is declared. When the Eastern Pacific Ocean is 0.5 degrees Celsius below normal for 5 consecutive 3-month average periods, a La Nina is declared.

The El Niño and La Nina are declared as Weak, Moderate, or Strong depending on how far from normal the water temperature gets. When the temperature is above 1.5 degrees Celsius, it is declared as strong. When the temperature is above 1.0 degrees Celsius, it is declared as Moderate. When the temperature is above 0.5 degrees Celsius, it is declared as Weak.

The effect on Ventura County trends to be wetter with El Niños and drier with La Ninas. Although the top driest years have been Neutral or Weak or Moderate El Niños.

Data for calculating ENSO Index (ONI) is provided by the Climate Prediction Center.