ENSO Outlook
An alert system for the El Niño–Southern Oscillation

The status of the ENSO Outlook is determined using set Criteria and expert analysis by climatologists at the Bureau of Meteorology.

El Niño and La Niña Outlook status

Details: Climate Driver Update

Fortnightly ENSO Outlook values

Monthly ENSO Outlook values

Legend

ENW El Niño Watch
LNA El Niño Alert
EN El Niño
N Inactive
LNW La Niña Watch
ENA La Niña Alert
LN La Niña

El Niño and La Niña years

Shading of text in the year column refers to years in which El Niño (red) or La Niña (blue) events began.

Past ENSO events

Historical values of the ENSO Outlook status prior to 2014 are based on the set criteria alone. Values from the beginning of 2014 include expert analysis by climatologists at the Bureau of Meteorology to make the final assessment on a status level having been reached.

El Niño criteria

El Niño Watch El Niño Watch

The chance of an El Niño developing in the coming season has increased. When these criteria have been met in the past, an El Niño event has developed around 50% of the time.

All of the following criteria need to be satisfied:

  1. Current climate state: ENSO phase is currently neutral or declining La Niña.
    • Either:
      SOI analogues: Of the 10 years that most closely resemble the current Southern Oscillation Index pattern, 4 or more have shown El Niño characteristics.
    • Or:
      Sub-surface: Significant sub-surface warming has been observed in the western or central equatorial Pacific Ocean.
  3. Models: One-third or more of surveyed climate models show sustained warming to at least 0.8 °C above average in the NINO3 or NINO3.4 regions of the Pacific Ocean by late winter or spring.

El Niño Alert El Niño Alert

The chance of an El Niño developing in the coming season has increased. When these criteria have been met in the past, an El Niño event has developed around 70% of the time.

Any three of the following criteria need to be satisfied:

  1. Sea surface temperature: A clear warming trend has been observed in the NINO3 or NINO3.4 regions of the Pacific Ocean during the past three to six months.
  2. Winds: Trade winds have been weaker than average in the western or central equatorial Pacific Ocean during any two of the last three months.
  3. SOI: The two-month average Southern Oscillation Index is –7 or lower.
  4. Models: A majority of surveyed climate models show sustained warming to at least 0.8 °C above average in the NINO3 or NINO3.4 regions of the Pacific Ocean by the late winter or spring.

El Niño El Niño

An El Niño has been declared and is underway.

Any three of the following criteria need to be satisfied:

  1. Sea surface temperature: Temperatures in the NINO3 or NINO3.4 regions of the Pacific Ocean are 0.8 °C warmer than average.
  2. Winds: Trade winds have been weaker than average in the western or central equatorial Pacific Ocean during any three of the last four months.
  3. SOI: The three-month average Southern Oscillation Index is –7 or lower.
  4. Models: A majority of surveyed climate models show sustained warming to at least 0.8 °C above average in the NINO3 or NINO3.4 regions of the Pacific until the end of the year.

La Niña criteria

La Niña Watch La Niña Watch

The chance of a La Niña developing in the coming season has increased. When these criteria have been met in the past, a La Niña event has developed around 50% of the time.

All the following criteria need to be satisfied:

  1. Current climate state: ENSO phase is currently neutral or declining El Niño.
    • Either:
      SOI analogues: Of the 10 years that most closely resemble the current Southern Oscillation Index pattern, 4 or more have shown La Niña characteristics.
    • Or:
      Sub-surface: Significant sub-surface cooling has been observed in the western or central equatorial Pacific Ocean.
  3. Models: One-third or more of surveyed climate models show sustained cooling to at least 0.8 °C below average in the NINO3 or NINO3.4 regions of the Pacific Ocean by late winter or spring.

La Niña Alert La Niña Alert

The chance of a La Niña developing in the coming season has increased. When these criteria have been met in the past, a La Niña event has developed around 70% of the time.

Any three of the following criteria need to be satisfied:

  1. Sea surface temperature: A clear cooling trend has been observed in the NINO3 or NINO3.4 regions of the Pacific Ocean during the past three to six months.
  2. Winds: Trade winds have been stronger than average in the western or central equatorial Pacific Ocean during any two of the last three months.
  3. SOI: The two-month average Southern Oscillation Index is +7 or higher.
  4. Models: A majority of surveyed climate models show sustained cooling to at least 0.8 °C below average in the NINO3 or NINO3.4 regions of the Pacific Ocean by the late winter or spring.

La Niña La Niña

A La Niña has been declared and is underway.

Any three of the following criteria need to be satisfied:

  1. Sea surface temperature: Temperatures in the NINO3 or NINO3.4 regions of the Pacific Ocean are 0.8 °C cooler than average.
  2. Winds: Trade winds have been stronger than average in the western or central equatorial Pacific Ocean during any three of the last four months.
  3. SOI: The three-month average Southern Oscillation Index is +7 or higher.
  4. Models: A majority of surveyed climate models show sustained cooling to at least 0.8 °C below average in the NINO3 or NINO3.4 regions of the Pacific Ocean until the end of the year.

 

Inactive criteria

El Niño and La Niña Neutral Inactive

An ENSO event is not active in the tropical Pacific Ocean and there are no signs of an El Niño or La Niña developing.

Using the ENSO Outlook

  • The purpose of the ENSO Outlook is to look ahead and assess the likely evolution of the El Nino-Southern Oscillation as it transitions through the different phases of ENSO (El Niño, La Niña and Neutral). It aims to forewarn the Australian community using a staged approach based on changes in the likelihood or risk of an El Niño or La Niña occurring.
  • The three stages of the ENSO Outlook are designed to reflect the level of confidence that climatologists and oceanographers have that an ENSO event may occur in the season ahead.
  • An El Niño Watch, for example, does not guarantee that an El Niño will develop – rather it indicates that the tropical Pacific Ocean is showing some signs that an El Niño may develop.
  • For a stage to be reached, Bureau of Meteorology climatologists assess whether a set of atmospheric and oceanic criteria have been met, and that the current state of the climate system has reached that status level.
  • When the ENSO Outlook reaches the Alert stage, both the ENSO Outlook and the Climate Driver Update may increase from fortnightly to weekly updates to ensure timely information is provided on the latest state of ENSO.
  • Once an ENSO Outlook status level is reached, it remains valid until it is either increased to the next level or cancelled, or if an ENSO event has been declared, the event officially declared over. This is done by climatologists at the Bureau of Meteorology.
  • Occasionally fluctuations in the atmosphere or oceans might mean that criteria that were met in the previous month may drop below criteria thresholds for the current month. Bureau climatologists determine whether or not this is likely to be a temporary fluctuation in which case the status will remain unchanged, or a permanent drop in the index, in which case the Watch or Alert may be cancelled.
  • During the autumn months (often regarded as the ENSO transition period) it is possible that two status levels may be reached at once (for example, in February 1988, both El Niño and La Niña Watch criteria were satisfied as an El Niño was coming to an end and a La Niña was starting to develop). The ENSO Outlook will display the developing event status from March, even if there is an event still active.

ENSO Outlook verification

The ENSO Outlook system has been retrospectively assessed for each year since 1980 with the success rate summarised below. Important considerations relating to these figures include:

  • The verification was undertaken using data that would have been available at the time. For example, when assessing for March 1982, only the monthly SOI and ocean temperature data up to and including February 1982 was used.
  • Limited model outlooks were available prior to 2000 so model hindcasts (i.e., running models based on past conditions) have been used to assess this criterion.
  • The final decision to declare an ENSO Outlook status level (e.g., El Niño Alert) is made by climatologists at the Bureau of Meteorology. As expert analysis by climatologists is not available for past assessments, the verification is based on the set criteria alone.
  • Since 1980 there have been nine El Niño and eight La Niña events; this is regarded as a small sample size from which to draw statistics.

ENSO Outlook status: success rate

  • Verification of the ENSO Outlook system found that for El Niño and La Niña events:
    • About 50% of the time a Watch was reached, an ENSO event subsequently occurred; and
    • About 70% of the time an Alert was reached, an ENSO event subsequently occurred.

About ENSO

Related sites

History

El Niño under way in the tropical Pacific

The ENSO Outlook has shifted to El Niño, having met criteria 1, 3 and 4 – see below.

Climate model outlooks suggest this El Niño is likely to continue until at least the end of the southern hemisphere summer 2023–24. The ENSO Outlook will remain at El Niño until this event decays, or signs of a possible La Niña appear. 

Product code: IDCKGEAS00