ENSO and IOD likely to remain neutral in spring

Weather Eye
with John Maunder

The El Niño–Southern Oscillation (ENSO) is currently neutral.

Sea surface temperatures (SSTs) in the central equatorial Pacific Ocean are ENSO-neutral, having gradually cooled from El Niño levels since December 2023.

This cooling is being sustained by deep waters surfacing in the central and eastern Pacific. Atmospheric patterns, including cloud and trade winds, remain largely ENSO-neutral.

Three of 7 climate models suggest the possibility of SSTs in the tropical Pacific exceeding the La Niña threshold (below −0.8 °C) from October, while the remaining 4 models, including the Bureau's, suggest SSTs are likely to remain at ENSO-neutral values (between −0.8 °C to +0.8 °C ) throughout the forecast period. This means it is possible a La Niña may develop in coming months.

The Indian Ocean Dipole (IOD) is currently neutral, with the latest weekly IOD index value (as of 1 September) of +0.15 °C. Most models indicate that the IOD is likely to remain neutral until at least the end of spring.

Global SSTs were the warmest on record for each month between April 2023 and June 2024. July 2024 global SSTs were the second warmest on record, not as warm as July 2023 but much warmer than any other year. August 2024 is currently tracking as the second-warmest August for SSTs on record.

The current global pattern of warmth differs to historical patterns of SSTs associated with ENSO and IOD. This means future predictions of ENSO and IOD based on SSTs during past events may not be reliable.

Phenomena such as ENSO and the IOD are only broad indicators of the expected climate. The long-range forecast provides better guidance on local rainfall and temperature patterns.

The Southern Annular Mode (SAM) is currently positive (as at 1 September), having been neutral for most of the second half of August.

The SAM index is forecast to become neutral during the coming week. A neutral SAM has no strong influence on Australian rainfall and temperature patterns.

A pulse of the Madden–Julian Oscillation (MJO) is currently in the Maritime Continent region to Australia's north (as at 1 September).

Most models suggest the pulse will either maintain its strength or strengthen slightly as the MJO progresses over the Maritime Continent in the coming week. When the MJO is in the Maritime Continent at this time of year, it may contribute towards strengthening trade winds, which can assist with La Niña development.

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Monthly ENSO Outlook values

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

  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1980 N N ENW ENW ENW ENW ENW N N N N N
1981 N N N N N N N N N N N N
1982 N N N N ENW ENA EN EN EN EN EN EN
1983 EN EN LNW LNW LNW LNW LNW LNW LNA LNA LN LN
1984 LN LNW LNW LNW LNW LN LN N N N N N
1985 N N LNA LNA N LN N N N N N N
1986 N N N N N N ENA ENA ENA ENA EN EN
1987 EN EN EN EN EN EN EN EN EN EN EN EN
1988 EN EN LNW LNA LNA LN LN LN LN LN LN LN
1989 LN LN LN ENW ENW N N N N N N N
1990 ENW ENW ENA ENA N N N N N N N N
1991 N N ENW N ENA EN EN EN EN EN EN EN
1992 EN EN EN EN EN EN N N N N N N
1993 N N ENA ENA EN EN N N N N N N
1994 N N N N ENW ENA N ENA N EN EN EN
1995 EN EN N LNW LNW LNW N LNA LN LN LN LN
1996 N N ENW ENW ENW ENW N N N N N N
1997 ENW ENW ENW ENW ENA EN EN EN EN EN EN EN
1998 EN EN LNW LNW LNW LNA LNA LN LN LN LN LN
1999 LN LN LN LN LN LN LN LN LN LN LN LN
2000 LN LN ENW ENW ENW ENW N N N LNA LNA LNA
2001 LN N ENW ENW ENW N ENW N N N N N
2002 N N ENW ENA ENA ENA EN EN EN EN EN EN
2003 EN N N N LNW LNW N N N N N N
2004 N N N N N N ENW ENA ENA ENA ENA ENA
2005 N N N ENW N N N N N N N N
2006 N N N N N N ENW ENA EN EN EN EN
2007 EN N LNW LNW LNA LNA LNA LN LN LN LN LN
2008 LN LN LNA LNA N N N N N N LNA LN
2009 LN LN ENW ENW ENW ENW ENW ENA ENA ENA EN EN
2010 EN EN EN LNW LNA LNA LN LN LN LN LN LN
2011 LN LN LN N N N N N LNA LN LN LN
2012 LN LN N N ENW ENW N N N N N N
2013 N N N N N N N N N N N N
2014 N ENW ENW ENA ENA ENA ENA ENW ENW ENW ENA ENA
2015 ENA N ENW ENA EN EN EN EN EN EN EN EN
2016 EN EN EN LNW LNW LNW LNW LNW LNW LNW LNW N
2017 N N ENW ENW ENW ENW N N N N LNW LN
2018 LN LN N N N ENW ENW ENW ENW ENA ENA ENA
2019 ENA ENW ENW ENA ENW ENW N N N N N N
2020 N N N N N N LNW LNW LNA LN LN LN
2021 LN LN LN N N N N N LNW LNA LNA LN
2022 LN LN LN LN LN LN LNW LNA LN LN LN LN
2023 LN LN ENW ENW ENW ENA ENA ENA EN EN EN EN
2024 EN EN EN N LNW LNW LNW LNW LNW na na na

Key

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

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.

- from Australian Bureau of Meteorology.

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