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

El Niño and La Niña Outlook status

Details: Climate Driver Update

The status of the ENSO Outlook is determined using set criteria (described below) and expert analysis by climatologists at the Bureau of Meteorology. It is updated fortnightly.

El Niño

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 SOI 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 SOI 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 SOI 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

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 SOI 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 SOI 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 SOI 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

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."

The ENSO Outlook status is updated each fortnight. The below graph shows the fortnightly values dating back to January 1980. The below table shows the monthly value of the ENSO Outlook for historical comparisons. The ENSO Outlook graph and table are not an official time-line of ENSO events. For the official history of El Niño and La Niña events see:

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.

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 ENSO Wrap-Up 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

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Eastern Pacific warms, but little atmospheric response

The ENSO Outlook is at El Niño WATCH. While the El Niño–Southern Oscillation (ENSO) is currently neutral, El Niño WATCH indicates there is an increased risk of an El Niño occurring this year, at least double the usual chance of 25%. 

Oceanic warming is continuing in the central and eastern tropical Pacific. However, the western Pacific also remains warmer than average.

We are starting to see some changes in the atmosphere but this needs to be sustained over several weeks or months. An accompanying shift in atmospheric circulation is necessary for an El Niño event to be declared.

While models are forecasting a very high likelihood that ocean temperatures in the central and eastern Pacific will reach El Niño thresholds in southern hemisphere winter, an accompanying shift in atmospheric circulation is necessary for an El Niño event to be declared. Due to the persistence of neutral atmospheric indicators over the tropical Pacific, our ENSO outlook remains at El Niño WATCH.

History shows that when the ENSO Outlook has reached El Niño WATCH, El Niño has subsequently developed in about half of those years.

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