What Is El Niño? El Niño is a term that refers to anomalously warmer than average Sea Surface Temperatures (SSTs) in the eastern and central equatorial Pacific Ocean. It is normally characterized by warming of the subsurface layers and large scale weakening of the trade winds in the region. These changes have important consequences over weather/climate around the globe, including East Africa.
La Nina Scientists refer to the event when exceptionally cool water lies off the coast of South America as La Nina Strong La Nina events have been responsible for the opposite effects on climate as El Nino.
Strongest El Niño's 4 Very strong El Nino events occurred in 1965-1966, 1982- 1983, and 1997-1998. They caused significant flooding and damage from California to Mexico to Chile. Effects of El Nino are felt as far away from the Pacific Ocean as Eastern Africa including Kenya. NB: An El Nino year correspond to the first three months of the ENSO year namely October, November, and December. For example, the ENSO year 1970 starts October 1970 and ends September 1971.
Strongest La Ninas 6 Strong La Nina events occurred in 1955-56, 1964-65, 1973-74, 1988-89 and 1998-2000. They were associated with drought over most parts of Eastern Africa including Kenya. NB: An La Nina year correspond to the first three months of the ENSO year namely October, November, and December. For example, the La Nina year of 1988 started in October 1988 and ended in September 1989.
Classification El Ninos & La Ninas 8 El Ninos & La Ninas are classified as either Weak, Moderate or Strong depending on the extent of warming/cooling in the Nino areas.
Sub-Surface Temperature Departures in the Equatorial Pacific
Since mid September, positive subsurface temperature anomalies have stretched across most of the equatorial Pacific. Recently, positive subsurface anomalies in the central Pacific are expanding eastward. Negative anomalies in the eastern Pacific are strengthening at depth.
Recent Evolution of Equatorial Pacific SST Departures (oC)
Average SST Departures (oC) in the Tropical Pacific During the Last Four Weeks
Weekly SST Departures during the Last Four Weeks During the last four weeks, positive SST anomalies persisted along the equatorial Pacific and strengthened in the eastern Pacific. From 15 October to 05 November 2014, equatorial SSTs were above average across most of the Pacific.
ONI (ºC): Evolution since 1950 The most recent ONI value (August – October 2014) is 0.2 o C.
CPC/IRI Probabilistic ENSO Outlook Updated: 6 November 2014 The chance of El Niño is 58% during the Northern Hemisphere winter and decreases into Spring/summer 2015.
IRI/CPC Pacific Niño 3.4 SST Model Outlook Most models favor El Niño (greater than or equal to +0.5ºC) to develop during October-December 2014 and persist through Northern Hemisphere spring 2015. Figure provided by the International Research Institute (IRI) for Climate and Society (updated 16 October 2014).
Summary ENSO Alert System Status: El Niño Watch ENSO-neutral conditions continue.* Positive equatorial sea surface temperature (SST) anomalies continue across most of the Pacific Ocean. There is a 58% chance of El Niño during the Northern Hemisphere winter, which is favored to last into the Northern Hemisphere spring 2015.*