Climate Driver Update
Climate drivers in the Pacific, Indian and Southern oceans and the Tropics

For rainfall and temperature long-range forecasts for Australia, please see our long-range forecast page. It provides the best guidance for likely conditions in the coming months, with the Bureau's climate model taking into account all influences from the oceans and atmosphere when generating its long-range forecasts. The Climate Driver Update provides insight into the state of the main drivers likely influencing current conditions.


Average of international model forecasts for NINO3.4

Average of international model forecasts for IOD


Sea surface temperature maps

Sea surface temperature maps are not available for forecasts before Spring 2018

Global sea surface temperature forecasts for the months and season ahead. Anomalies indicate the difference from normal.

Sea surface temperature maps (select map for larger view)

SST forecasts for the next 3 months

Pacific Ocean

ENSO is the oscillation between El Niño and La Niña states in the Pacific region. El Niño typically produces drier seasons, and La Niña drives wetter years, but the influence of each event varies, particularly in conjunction with other climate influences.

NINO3.4 SST plumes from Bureau model forecasts, updated daily
Select to see full-size map of NINIO3.4 SST plumes from Bureau model forecasts, updated daily.

International climate model forecasts

Nino 3.4 2 month forecast
Graph details

The graphs are based on the ensemble mean for the most recent model run.

These graphs show the average forecast value of NINO3.4 for each international model surveyed for the selected calendar month. If the bars on the graph are approaching or exceeding the blue dashed line, there is an increased risk of La Niña. Similarly, if the bars on the graph are approaching or exceeding the red dashed line, there is an increased chance of El Niño.

Weekly sea surface temperatures

Graphs of the table values

Monthly sea surface temperatures

Graphs of the table values

5-day sub-surface temperatures

Monthly temperatures

Southern Oscillation Index

30-day SOI values for the past two years
Select to see full-size map of 30-day Southern Oscillation Index values for the past two years, updated daily.

Trade winds

5-day SST and wind anomaly from TAO/TRITON
Select to see full-size map of 5-day SST and wind anomaly from TAO/TRITON.

Cloudiness near the Date Line

About El Niño and La Niña (ENSO)

El Niño Southern Oscillation

At a glance

ENSO is the oscillation between El Niño and La Niña conditions.

This climate influence is related to:   El Niño   La Niña   The Australian Monsoon

What is it?

The term El Niño refers to the extensive warming of the central and eastern tropical Pacific Ocean which leads to a major shift in weather patterns across the Pacific. This occurs every three to eight years and is associated with a weaker Walker Circulation (see diagram below) and drier conditions in eastern Australia. El Niño Southern Oscillation(ENSO) is the term used to describe the oscillation between the El Niño phase and the La Niña, or opposite, phase.

In the eastern Pacific, the northward flowing Humbolt current brings cooler water from the Southern Ocean to the tropics. Furthermore, along the equator, strong east to southeasterly Trade winds cause the ocean currents in the eastern Pacific to draw water from the deeper ocean towards the surface, helping to keep the surface cool. However in the far western Pacific there is no cool current, and weaker Trades mean that this "upwelling" effect is reduced. Hence waters in the western equatorial Pacific are able to warm more effectively under the influence of the tropical sun. This means that under "normal" conditions the western tropical Pacific is 8 to 10°C warmer than the eastern tropical Pacific. While the ocean surface north and northeast of Australia is typically 28 to 30°C or warmer, near South America the Pacific Ocean is close to 20°C. This warmer area of ocean is a source for convection and is associated with cloudiness and rainfall.

However, during El Niño years, the trade winds weaken and the central and eastern tropical Pacific warms up. This change in ocean temperature sees a shift in cloudiness and rainfall from the western to the central tropical Pacific Ocean.

Neutral ENSO phase

Trade winds push warm surface water to the west and help draw up deeper, cooler water in the east. The warmest waters in the equatorial Pacific build up to the north of Australia and that area become the focus for cloudiness and rainfall.

Map diagram of Neutral ENSO

La Niña

Trade winds strengthen, increasing the temperature of the warm water north of Australia. Cloudiness and rainfall north of Australia are enhanced, typically leading to above average winter–spring rainfall for eastern and central parts of the country, and a wetter start to the northern wet season.

Map diagram of Negative ENSO

El Niño

Trade winds weaken (or reverse) and warmer surface water builds up in the central Pacific. Cloudiness and rainfall north of Australia are supressed, typically leading to below average winter–spring rainfall for eastern parts of the country, and a drier start to the northern wet season.

Map diagram of Positive ENSO

The Southern Oscillation Index, or SOI, gives an indication of the development and intensity of El Niño or La Niña in the Pacific Ocean. The SOI is calculated using the pressure differences between Tahiti and Darwin. The following figure demonstrates the typical fluctuations in SOI over a period of 11 years. Positive SOI values are shown in blue, with negative in orange. Sustained positive values are indicative of La Niña conditions, and sustained negative values indicative of El Niño conditions.

See: Monthly SOI graph and data.

 

How does it affect Australia?

Each phase of the ENSO has a very different effect on the Australian climate. El Niño and La Niña generally have an autumn to autumn pattern of evolution and decay. That is, they typically begin to develop during autumn, strengthen in winter/spring, then decay during summer and autumn of the following year. These effects are described in further detail on the following pages: El Niño and La Niña.

Further information and latest updates

Further information about the El Niño Southern Oscillation and its impact on the Australian Climate.

  • The Climate Driver Update provides the latest information on the state of ENSO and the likely effect this will have on Australia.

Timeline of monthly Southern Oscillation Index (SOI) values since 1876

Timeline graph of ENSO and SOI index

Sustained negative values (bottom/yellow) of the SOI below −7 may indicate El Niño, while sustained positive values above +7 may indicate La Niña. La Niña and El Niño events since 1900 are indicated on the graph.
Drag graph slider to see full history and y-axis scale.


The Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperatures between the eastern and western tropical Indian Ocean. A negative phase typically sees above average winter-spring rainfall in Australia, while a positive phase brings drier than average seasons.

IOD SST plumes from Bureau model forecasts, updated daily
Select to see full-size map of IOD SST plumes from Bureau model forecasts, updated daily.

International climate model forecasts

Latest IOD forecast
Graph details

The graphs are based on the ensemble mean for the most recent model run.

Thse graphs show the average forecast value of the IOD index for each international model surveyed for the selected calendar month. If the majority of models are approaching or exceeding the blue dashed line, then there is an increased risk of a negative IOD event. If the majority of models are approaching or exceeding the red dashed line, then there is an increased risk of a positive IOD event.

  1. 1960
  2. 1961
  3. 1963
  4. 1967
  5. 1972
  6. 1975
  7. 1990
  8. 1992
  9. 1994
  10. 1996
  11. 1997
  12. 1998
  13. 2006
  14. 2010
  15. 2015
  16. 2016
  17. 2019
  18. 2022
Since 1960, when reliable records of the IOD began, to 2023,
there have been 9 moderate to strong negative IOD events and 9 moderate to strong positive IOD events.

About the Indian Ocean Dipole (IOD)

Indian Ocean sea surface temperatures impact rainfall and temperature patterns over Australia. Warmer than average sea surface temperatures can provide more moisture for frontal systems and lows crossing Australia.

Indian Ocean Dipole

Sustained changes in the difference between sea surface temperatures of the tropical western and eastern Indian Ocean are known as the Indian Ocean Dipole or IOD. The IOD is one of the key drivers of Australia's climate and can have a significant impact on agriculture. This is because events generally coincide with the winter crop growing season. The IOD has three phases: neutral, positive and negative. Events usually start around May or June, peak between August and October and then rapidly decay when the monsoon arrives in the southern hemisphere around the end of spring.


Neutral IOD phase

Water from the Pacific flows between the islands of Indonesia, keeping seas to Australia's northwest warm. Air rises above this area and falls over the western half of the Indian Ocean basin, blowing westerly winds along the equator.

Temperatures are close to normal across the tropical Indian Ocean, and hence the neutral IOD results in little change to Australia's climate.

Map diagram of Neutral IOD

Positive IOD phase

Westerly winds weaken along the equator allowing warm water to shift towards Africa. Changes in the winds also allow cool water to rise up from the deep ocean in the east. This sets up a temperature difference across the tropical Indian Ocean with cooler than normal water in the east and warmer than normal water in the west.

Generally this means there is less moisture than normal in the atmosphere to the northwest of Australia. This changes the path of weather systems coming from Australia's west, often resulting in less rainfall and higher than normal temperatures over parts of Australia during winter and spring.

Map diagram of Positive IOD

Negative IOD phase

Westerly winds intensify along the equator, allowing warmer waters to concentrate near Australia. This sets up a temperature difference across the tropical Indian Ocean, with warmer than normal water in the east and cooler than normal water in the west.

A negative IOD typically results in above-average winter–spring rainfall over parts of southern Australia as the warmer waters off northwest Australia provide more available moisture to weather systems crossing the country.

Map diagram of Negative IOD


Indian Ocean Dipole years

  1. 1960
  2. 1961
  3. 1963
  4. 1967
  5. 1972
  6. 1975
  7. 1990
  8. 1992
  9. 1994
  10. 1996
  11. 1997
  12. 1998
  13. 2006
  14. 2010
  15. 2015
  16. 2016
  17. 2019
  18. 2022
Since 1960, when reliable records of the IOD began, to 2023,
there have been 9 moderate to strong negative IOD events and 9 moderate to strong positive IOD events.

The Southern Annular Mode, or SAM, refers to the north-south shift of rain-bearing westerly winds and weather systems in the Southern Ocean compared to the usual position.


Southern Annular Mode (SAM) history

About the Southern Annular Mode (SAM) forecast

Southern Annular Mode

At a glance

The Southern Annular Mode can result in enhanced rainfall in regions of southern Australia.

This climate influence is related to:   ENSO   Frontal Systems

What is it?

The Southern Annular Mode, or SAM, also known as the Antarctic Oscillation (AAO), is a mode of variability which can affect rainfall in southern Australia. The SAM refers to the north/south movement of the strong westerly winds that dominate the middle to higher latitudes of the Southern Hemisphere. The belt of strong westerly winds in the Southern Hemisphere is also associated with the storm systems and cold fronts that move from west to east.

During the summer and autumn months (December through to May) the SAM is showing an increasing tendency to remain in a positive phase, with westerly winds contracted towards the south pole.

The contribution that the SAM makes to the climate variability in Australia and the apparent positive trend in the SAM are relatively recent discoveries and as such are still active areas of research.

SAM summer negative phase

Map diagram of Neutral sam

SAM summer positive phase

Map diagram SAM summer positive phase

SAM winter negative phase

Map diagram of SAM winter negative phase

SAM winter positive phase

Map diagram of SAM winter positive phase

Where, when and for how long does it occur?

 

Where, when and for how long does the Southern Annular Mode occur?

The diagram above shows the area affected by the Southern Annular Mode, when it occurs and how long it may last.

 

In terms of mean sea level pressure, the SAM affects the coastal regions of southern Australia throughout the year. Extreme negative phases of the SAM can cause increased rainfall and cold air outbreaks in southern Australia.

Each SAM event, both positive and negative, tends to last for around ten days to two weeks. The time frame between positive and negative events however is quite random, but is typically in the range of a week to a few months.

How does it affect Australia?

The impact that the SAM has on rainfall varies greatly depending on season and region. If Australia were a few degrees further south, then the impact of changes in SAM would be much more pronounced. The diagram below describes the average impact on rainfall during a "positive" (westerly winds further south) SAM event.

The SAM also has an impact on temperatures. In general, in areas where rainfall is increased, temperature is decreased whilst where rainfall is decreased, temperature is increased.

 

diagram showing the impact of the SAM

The diagram above shows the impact that a "positive" SAM event (decreased westerly winds) has on Australian rainfall. Shading indicates daily rainfall anomaly in mm/day for each of the seasons. (Source: Hendon et al. 2007)

 

An example

rainfall deciles thumbnail image

During July 2007, the SAM was in a strong negative phase. This was reflected in rainfall patterns across southern Australia.

Read more.

Further information and latest updates

 

The Madden–Julian Oscillation (MJO) is the major fluctuation in tropical weather on weekly to monthly timescales. It can be characterised as an eastward moving 'pulse' of cloud and rainfall near the equator that typically recurs every 30 to 60 days.

These charts are updated more frequently than Climate Driver Update editions, so may be more current than the MJO issue text (above).

Forecast MJO location and strength

The chart shows the strength and progression of the MJO through 8 different areas along the equator around the globe.
Area 3 is north west of Australia, 4 and 5 are to the north (the Maritime Continent), and 6 is to the north east.

RMM1 and RMM2 are mathematical methods that combine cloud amount and winds at upper and lower levels of the atmosphere to provide a measure of the strength and location of the MJO. When this index is within the centre circle the MJO is considered weak. Outside of this circle the index is stronger and will usually move in an anti-clockwise direction as the MJO moves from west to east.


Select to see full-size map of MJO phase, updated daily.

Madden–Julian Oscillation (MJO) phase chart

Tropical atmospheric waves

About tropical waves

MJO

The Madden–Julian Oscillation (MJO) is the major fluctuation in tropical weather on weekly to monthly timescales. It can be characterised as an eastward moving pulse or wave of cloud and rainfall near the equator that typically recurs every 30 to 60 days.

Other tropical waves in the atmosphere

In addition to the MJO, other large-scale atmospheric waves also occur in the tropics. The main ones are the convectively-coupled Kelvin wave (KW), equatorial Rossby wave (ER), and mixed Rossby-Gravity wave (MRG). They can provide further insight into the current tropical weather, such as the location and development of tropical cyclones, and what may occur over the coming days to weeks. These waves occur year-round, but typically have a greater influence on tropical weather in the Australian region during the wet-season months of October to April.

Kelvin wave (KW)

Equatorial Kelvin waves are alternating low and high pressure centres along the equator that move from west to east. For consistency with the theoretical structure of Kelvin waves, convection (leading to cloudiness and rainfall) near the equator should be on the western side of the low pressure regions. In contrast, clear conditions should be found on the eastern side of the low pressure. Like other atmospheric tropical waves, alternating zones of cloudiness and clear weather can be seen on satellite imagery in association with an active Kelvin wave. The waves move in the same direction as the Madden–Julian Oscillation, from west to east, but typically 2 to 3 times faster.

Per figure caption
Schematic depiction of the theoretical solution for an equatorial Kelvin wave in a dry, incompressible atmosphere

Equatorial Rossby (ER) wave

In theory there are several different equatorial Rossby waves. The most commonly seen atmospheric ER wave, and the one we discuss here, has high and low pressure regions centred at latitudes about 10 degrees north and south of the equator. To be consistent with theory, the lows and highs should form a symmetric pattern about the equator. Due to the wind flow around these high and low pressure regions, some regions along the equatorial zone favour cloud and rain formation, while other regions favour stable, clear conditions. On satellite imagery equatorial Rossby waves can often be identified due to the presence of cloud systems at similar longitudes on both sides of the equator. These cloud systems, in conjunction with the off-equatorial low pressure, can be the precursors to tropical cyclones on either side of the equator. While equatorial Rossby waves move at a speed close to that of a typical Madden–Julian Oscillation pulse, they move in the opposite direction—from east to west.

Per figure caption
Schematic depiction of the theoretical solution for an equatorial Rossby wave in a dry, incompressible atmosphere. Only one wavelength is drawn here.

Mixed Rossby-Gravity (MRG) wave

Like equatorial Rossby waves, mixed Rossby-Gravity waves also move towards the west, but MRG waves have their pressure centres arranged anti-symmetrically on either side of the equator. This means a low pressure centre on one side of the equator will be opposite a high pressure centre in the other hemisphere. Satellite analysis of mixed Rossby-Gravity waves shows favoured zones for deep convection, often with thunderstorm clusters, in an antisymmetric arrangement about the equator. Their speed of movement to the west is faster than that of an ER wave.

Per figure caption
Schematic depiction of the theoretical solution for a mixed Rossby-gravity wave in a dry, incompressible atmosphere (upper) and with moist convection (lower)

Images are from The COMET® Program, from Introduction to Tropical Meteorology.
The COMET® Website is at http://meted.ucar.edu/ of the University Corporation for Atmospheric Research (UCAR), sponsored in part through cooperative agreement(s) with the National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce (DOC). © 1997–2021 University Corporation for Atmospheric Research. All Rights Reserved.

MJO waves
Tropical atmospheric wave maps

MJO location and strength

These graphs show the strength and progression of the MJO through 8 different areas along the equator around the globe.
Area 3 is north west of Australia, 4 and 5 are to the north (the Maritime Continent), and 6 is to the north east.

RMM1 and RMM2 are mathematical methods that combine cloud amount and winds at upper and lower levels of the atmosphere to provide a measure of the strength and location of the MJO. When this index is within the centre circle the MJO is considered weak. Outside of this circle the index is stronger and will usually move in an anti-clockwise direction as the MJO moves from west to east.

MJO phase diagram
MJO phase diagram

*Note: There are missing satellite observations from 16/3/1978 to 31/12/1978.
Methodology: Until the end of 2013 we use the exact method of Wheeler and Hendon (2004, https://doi.org/10.1175/1520-0493(2004)132%3C1917:AARMMI%3E2.0.CO;2) and from 2014 we use the modified method of Gottschalck et al. (2010, https://doi.org/10.1175/2010BAMS2816.1).

Average weekly rainfall probabilities

These maps show average weekly rainfall probabilities for each of the 8 MJO phases. Green shades indicate higher than normal expected rainfall, while brown shades indicates lower than normal expected rainfall.

Select the 'Wind' checkbox to also show the expected 850 hPa (approximately 1.5 km above sea level) wind anomalies. The direction and length of the arrows indicate the direction and strength of the wind anomaly. The darker the arrow, the more reliable the information is.

The relationship of the MJO with global weather patterns changes with the season.
Read more: The Combined Influence of the Madden–Julian Oscillation and El Niño–Southern Oscillation on Australian Rainfall.

Global maps of outgoing longwave radiation (OLR)

Global maps of outgoing longwave radiation (OLR) highlight regions experiencing more or less cloudiness. The top panel is the total OLR in Watts per square metre (W/m²) and the bottom panel is the anomaly (current minus the 1979-1998 climate average), in W/m². In the bottom panel, negative values (blue shading) represent above normal cloudiness while positive values (brown shading) represent below normal cloudiness.

Maps of total and anomaly outgoing longwave radiation (OLR)

Regional timeseries charts of outgoing longwave radiation (OLR)

The charts linked from this map show the OLRs for the different regions within the Darwin RSMC area. The horizontal dashed line represents what is normal for that time of year (based on the 1979 to 1998 period). The coloured curve is the 3-day moving average OLR in W/m². Below normal OLR indicates cloudier than normal conditions in this particular area, and is shown in blue shading. Above normal OLR indicates less cloudy conditions and is shown in yellow shading.

Tap boxes to view a timeseries chart of cloudiness for that region
image/svg+xml Southern India and Sri Lanka Southern India and Sri Lanka Indochina Indochina Philippines Philippines Malaysia and Indonesia Malaysia and Indonesia Guam and Marianas Guam and Marianas Micronesia Micronesia Northern Australia Northern Australia Coral Sea Coral Sea Vanuatu Vanuatu Fiji Fiji New Guinea New Guinea Solomon Islands Solomon Islands Nauru and Tuvalu Dateline Dateline

Time longitude plots

Time longitude plots of daily averaged OLR anomalies (left) and 850 hPa (approximately 1.5 km above sea level) westerly wind anomalies (right) are useful for indicating the movement of the MJO.

How to read the Time longitude plots

The vertical axis represents time with the most distant past on the top and becoming more recent as you move down the chart. The Horizontal axis represents longitude.

Eastward movement of a strong MJO event would be seen as a diagonal line of violet (downward from left to right) in the OLR diagram, and a corresponding diagonal line of purple in the wind diagram. These diagonal lines would most likely fall between 60°E and 150°E and they would be repeated nearly every 1 to 2 months.

Daily averaged OLR anomalies

Daily averaged OLR anomalies

Westerly wind anomalies

Westerly wind anomalies

Sea surface temperatures (SSTs) for April 2024 were warmer than average across most of the tropical Pacific Ocean west of 120 °W. Between 20°S and 10°N, SST anomalies were more than 0.8 °C warmer than the long-term (1961–1990) average in most of the central and western Pacific Ocean. The extent and magnitude of warm anomalies across the equatorial Pacific has decreased compared to March 2024, reflecting the decay of El Niño to neutral El Niño–Southern Oscillation (ENSO) conditions.

Warm SST anomalies up to 2 °C above average also continued off most of the south-eastern Australian coast, increasing to up to 3 °C above average in a small area east of Tasmania. When compared to March 2024, SST anomalies have generally decreased, especially in the Coral Sea. Warm anomalies persist in the Maritime Continent, particularly in its northern region and to the west and south of WA.

The Bureau's long-range forecasts indicate warmer than average SSTs (reaching 2 °C warmer than average) will likely continue surrounding Australia, and SSTs up to 3 °C warmer than average in the Tasman Sea and south-west of Australia during June to August.

For the week ending 12 May 2024, sea surface temperatures (SSTs) were warmer than the 1961–1990 average across much of the equatorial Pacific Ocean west of 150 °W. There is an area of cooler than average water in the eastern equatorial Pacific, surrounding 120 °W. Compared to last fortnight, this region of cooler than average water has increased in area.

Closer to Australia, SSTs were 0.8 to 2 °C warmer than usual off much of Australia's eastern coastline, and around the Maritime Continent. SSTs were up to 4 °C warmer than usual south of Tasmania. SSTs surrounding Australia have mostly increased in magnitude compared to last fortnight.  

Across the Atlantic Ocean basin, there is exceptional and prolonged warmth in SSTs. Broad regions within 30°S to 60°N are exhibiting anomalies that are 1.2 to 3 °C warmer than average, with slightly smaller areas of positive anomalies further north to 60°N. Anomalies remain similar to the previous fortnight.

The latest values of the three NINO indices in the Bureau dataset for the week ending 12 May 2024 are: NINO3, +0.20 °C; NINO3.4, +0.45 °C; and NINO4, +0.80 °C. These values reflect historically neutral ENSO conditions.

The 30–, 60– and 90-day Southern Oscillation Index (SOI) for the period ending 12 May 2024 were −3.0, −2.8 and −0.8, respectively. The SOI reflects neutral ENSO conditions.  

Trade winds for the 5 days ending 12 May 2024 were mostly close to average over most of the equatorial Pacific and slightly stronger than average over the central Pacific.   

During an El Niño event, there is typically a sustained strengthening of trade winds across much of the equatorial Pacific.

The Madden–Julian Oscillation (MJO)  is currently weak. Most models forecast indicate that the MJO will remain weak before re-strengthening over the eastern Indian Ocean or Maritime Continent region from mid- to late-May. When the MJO is in the eastern Indian Ocean or Maritime Continent or at this time of the year, it typically acts to increase rainfall across parts of north-eastern and coastal eastern Australia. Tropical regions north of Australia usually also see an increase in cloudiness and rainfall.

The Indian Ocean Dipole (IOD) is currently neutral. The most recent value of the IOD index (+0.22 °C) is the second consecutive weekly value within historically neutral thresholds. This follows 7 weeks of the index being above the positive IOD threshold (+0.40 °C). Typically, a positive IOD event is considered underway once the IOD index is sustained above +0.40 °C for about 8 weeks.

Atmospheric indicators in March and April also indicated that a positive IOD event may have been developing. However, the latest SST and atmospheric observations suggest any potential development may have stalled. If a positive IOD develops, it would be earlier in the calendar year than is typical historically.

Bureau modelling suggests positive IOD conditions in May and into winter. However, the latest forecasts are suggesting a weaker positive IOD than earlier forecasts. At this time of year, historical skill of IOD forecasts beyond autumn is low.

Sea surface temperatures (SSTs) for the week ending 12 May 2024 were 0.8 to 2 °C warmer than the 1961–1990 average across much of the Indian Ocean. In the eastern tropical Indian Ocean south of the equator, SSTs are 0.4 to 1.2 °C warmer than average, and the central tropical Indian Ocean, warming slightly over the past fortnight.

Closer to Australia, SSTs are up to 3 °C warmer than average off the southern west coast of Australia and close to average north-west of WA. Compared to the previous fortnight, SSTs off the south-west coast have warmed while SSTs to the north-west of Australia remain similar.

Cloudiness near the equatorial Date Line is currently close to average. Cloudiness has been slightly above average for most of May to date.

Equatorial cloudiness near the Date Line typically increases during El Niño (below average OLR) and decreases during La Niña (above average OLR).

The 4-month sequence of equatorial Pacific sub-surface temperature anomalies (to 30 April 2024) shows patches of weak warm anomalies of up to 1.5 °C warmer than average across the top 50 m of the central and western equatorial Pacific during April. Cool anomalies are present below this shallow layer and exceed more than 3.5 °C cooler than average eastwards of 160 °W and rise eastwards to the top 50 to 100m of the eastern Pacific where anomalies are up to 2 °C cooler than average.

The depth and magnitude of warm anomalies has significantly decreased over the December to April period. The magnitude and extent of cool anomalies has also increased and has spread eastwards over the December to March period. From March to April, the extent of cool anomalies remains similar, while the peak magnitude has decreased. The presence of a substantial layer of cooler than average waters near the surface suggests some cooling of the surface is likely over the next few months.

For the 5 days ending 12 May 2024, cooler than average water persists from 150 to 275 m depth in the western Pacific sub-surface, rising to 50 to 100 m in the eastern Pacific sub-surface. Much of this region is 1 to 4 °C cooler than average. Cooler waters peak around 100 to 175 m depth in the central Pacific where they are up to 6 °C cooler than average. The magnitude of the cool anomalies has increased compared to the previous fortnight.

In the top 25 m of the eastern equatorial Pacific, slightly warm anomalies of up to 2 °C warmer than average remain and have slightly increased in magnitude during the past fortnight.

The El Niño–Southern Oscillation (ENSO) is currently neutral. There are some early signs that a La Niña might form in the Pacific Ocean later in 2024. As a result, the Bureau's ENSO Outlook has shifted to La Niña Watch. When La Niña Watch criteria have been met in the past, a La Niña event has subsequently developed around 50% of the time. There is about an equal chance of neutral ENSO conditions in the same outlook period.

Sea surface temperatures (SSTs) in the central Pacific have been steadily cooling since December 2023. This surface cooling is supported by a significant amount of sub-surface cooling in the central and eastern Pacific. Recent cloud and surface pressure patterns are ENSO-neutral.

The Bureau's modelling suggests that ENSO will likely remain neutral until at least July 2024. It is important to emphasise that early signs of La Niña are most relevant to the climate of the tropical Pacific, and that the long-range forecast for Australian rainfall and temperature provides better guidance for local climate.

The Indian Ocean Dipole (IOD) is currently neutral. The most recent 2 weeks have seen the IOD index within neutral thresholds, and follow 7 weeks of the index being above the positive IOD threshold (+0.40 °C). The current SST observations suggest that recent development of a positive IOD may have stalled. If a positive IOD eventually develops, it would be earlier in the calendar year than is typical historically.

Global sea surface temperatures (SSTs) have been the warmest on record for each month between April 2023 and April 2024, with April 2024 SSTs warmer than April 2023. The global pattern of warmth is affecting the typical historical global pattern of sea surface temperatures associated with ENSO and IOD variability.  As the current global ocean conditions have not been observed before, inferences of how ENSO or IOD may develop in 2024 that are based on past events may not be reliable.

The Southern Annular Mode (SAM) is currently neutral (as at 13 May). Forecasts indicate the index is mostly likely to remain neutral or become positive in the coming fortnight.

The Madden–Julian Oscillation (MJO) is currently weak. Most models forecast indicate that the MJO will remain weak before re-strengthening over the eastern Indian Ocean or Maritime Continent region from mid- to late-May.

The Southern Annular Mode (SAM) is currently neutral (as at 14 May). It is expected to remain neutral or become positive in the coming fortnight. A neutral SAM has little influence on Australian climate.

The Bureau's modelling suggests that ENSO will likely remain neutral until at least July 2024. Although ENSO forecast skill has historically increased after mid-autumn, model forecasts are still showing a spread of possible conditions.

Product code: IDCKGEWW00

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