The Oceanic Ni ñ o Index (ONI) has become the de-facto standard that NOAA uses for classifying El Ni ñ o (warm) and La Ni ña (cool) events in the eastern tropical Pacific. It is the running 3-month mean SST anomaly for the Ni ñ o 3.4 region (i.e., 5 o N-5 o S, 120 o -170 o W).

Note the major La Niña in 1988-1999, and major El Niños in 1996-1997 and 2015-2016. Years are marked on the left side, with 1986 at the top and the latest year at the bottom; Both panels show sea surface temperature along the equator in Pacific Ocean, with Indonesia on the left (west) and South America on the right (east).

Episodes of El Niño and La Niña typically last nine to 12 months, but can sometimes last for years. El Niño and La Niña events occur every two to seven years, on average, but they don’t occur on a regular schedule.

Top 24 Strongest El Niño and La Niña Event Years by Season. The values below were calculated using PSL's Extended Multivariate ENSO Index (MEI.ext) for 1895 to 2015.

Jan 18, 2016 · Both El Niño and La Niña can last more than a year, but it is rare for El Niño events to last longer than a year or so, while it is common for La Niña to last for two years or more. The longest El Nino in the modern record lasted 18 months, while …

Temporal evolution of El Niño and La Niña events indicated by the MEI.v2. Shown are the top 5 warm and cold non-overlapping events since 1979. Year 0 corresponds to the year of the event in the legends. Click on image to enlarge.

WE=Weak El Niñ o, ME=Moderate El Ni ñ o, SE=Strong El Niño, VSE=Very Strong El Niño WL=Weak La Ni ñ a, ML=Moderate La Ni ñ a, SL=Strong La Ni ña ENSO Type

Mar 13, 2025 · La Niña conditions persisted through February, but forecasters expect ENSO-neutral conditions to develop in the next month and persist through the Northern Hemisphere summer.. ENSO. La Niña is the cool phase of the El Niño/Southern Oscillation, or ENSO, a pattern of changes in the tropical Pacific Ocean and the atmospheric circulation over the tropical Pacific that persists for many months.

Mar 13, 2025 · El Niño and La Niña are the warm and cool phases of a natural climate pattern across the tropical Pacific known as the El Niño-Southern Oscillation, or “ENSO” for short. The pattern shifts back and forth irregularly every two to seven years, bringing predictable changes in ocean temperature and disrupting the normal wind and rainfall ...

El Niño-Southern Oscillation (ENSO) exhibits a strong asymmetry between warm El Niño and cold La Niña in amplitude and temporal evolution. An El Niño often leads to a heat discharge in the equatorial Pacific conducive to its rapid termination and transition to a La Niña, whereas a La Niña persists and recharges the equatorial Pacific for consecutive years preconditioning development of …