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 events 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.

 

graph of SOI

This graph shows the values of the SOI between 1991 and mid-2015. Monthly SOI data.

 

How does it affect Australia?

Each phase of the ENSO has a very different effect on the Australian climate. Events 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 east 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 and a change to RMM methods in 2014.

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 January 2024 were warmer than average across the tropical Pacific Ocean. Between 10°S and 10°N, SST anomalies were more than 1.2 °C warmer than the long-term (1961–1990) average in most areas along the equator.

The extent and magnitude of warm anomalies across the equatorial Pacific has decreased east of the Date Line compared to December 2023, while warm anomalies increased west of the Date Line.

Warm SST anomalies also continued off most of the eastern Australian coast from central Queensland southwards, and around Tasmania and the Tasman Sea. When compared to December 2023, SST anomalies have increased over the Coral Sea region off the Queensland coast. Warm anomalies were also present through parts of the Southern Ocean south of Western Australia and have warmed further compared to December 2023. Small regions of cool normal anomalies, up to 1.2 °C below the 1961–1990 average, were present in the Great Australian Bight.

In the Indian Ocean, cool anomalies were present off the Pilbara coast in Western Australia, with SST anomalies in a narrow band along most the Western Australian coast having cooled when compared to December 2023. Warm anomalies persist in the Maritime Continent, particularly the north of that region, with a significant increase in warm SST anomalies occurring in a small region off the Sumatra coast, where anomalies were more than 2 °C warmer than they were compared to the previous month; this warming is in line with the decay of the 2023 positive IOD event.

The Bureau's long-range forecasts indicate warmer than average SSTs (reaching 1.2 °C warmer than average) will likely continue off the coast of northern and eastern Australia through till at least March.

For the week ending 18 February 2024, sea surface temperatures (SSTs) were warmer than average across the equatorial region of the tropical Pacific Ocean, with anomalies more than 1.2 °C warmer than average in areas east of 160 °E along the equator. Large regions of warm anomalies between 0.8 °C and 2 °C extended across much of the off-equatorial South Pacific eastwards from Australia to French Polynesia at 160 °W.

Closer to Australia, warm SST anomalies of 1.2 °C to 2 °C extend across much of the western Pacific Ocean, around Australia's eastern, western, and southern coastlines, and patches of the Maritime Continent. SST anomalies more than 2 °C above average were also present in the Tasman Sea and south of Tasmania. Small regions close to the coast of the Great Australian Bight have cool SST anomalies, up to 2 °C below average.

Compared to last fortnight, SSTs anomalies off the coast of the Great Australian Bight, around the Coral Sea, and in the central and eastern Pacific, have continued to cool.

The latest values of the three NINO indices for the week ending 18 February 2024 were: NINO3, +1.27 °C; NINO3.4, +1.26 °C; and NINO4, +1.12 °C.

Persistent NINO3 or NINO3.4 values warmer than +0.8 °C are typical of El Niño, while persistent values cooler than –0.8 °C typically indicate La Niña.

The 30–, 60– and 90-day Southern Oscillation Index (SOI) values for the period ending 18 February 2024 were −17.1, −6.2 and −4.3, respectively. All SOI values are more negative compared to two weeks ago. 30-day SOI can have increased variability in the southern hemisphere summer due to local weather systems over northern Australia or Tahiti.

Trade winds for the 5 days ending 18 February 2024 were generally close to average over most of the Pacific. There was a small area of weaker than average trade winds south of the equator, around 170°W, which was likely associated with an active Madden Julian Oscillation (MJO) that has since weakened.

During an El Niño event, there is typically a sustained weakening, or even reversal, of trade winds across much of the tropical Pacific.

The Madden–Julian Oscillation (MJO) has weakened significantly in the central Pacific Ocean in the past week and is now weak or indiscernible.  All international climate models indicate the MJO will remain weak in the coming week, with some models suggesting a strengthening in Maritime Continent at the start of March.

The Indian Ocean Dipole (IOD) is currently neutral, with the IOD index being −0.05 °C for the week ending 18 February 2024.

International climate models surveyed by the Bureau suggest IOD values will remain neutral until at least April.

Sea surface temperatures (SSTs) for the week ending 18 February were up to 2 °C warmer than the 1961–1990 average across much of the tropical Indian Ocean, with warm anomalies also extending south-eastwards to waters south of Australia. Compared to last fortnight, waters in the eastern Indian Ocean have continued to warm.

Outgoing Longwave Radiation (OLR) around the equatorial Date Line is currently below average (indicating increased cloudiness). OLR was mostly below average since mid-September 2023, tending positive for most of January 2024, before returning to below average values since late January.

Equatorial cloudiness near the Date Line typically increases during El Niño (negative OLR anomalies).

The 4-month sequence of equatorial Pacific sub-surface temperature anomalies (to 31 January 2024) shows warm anomalies across most of the top 50 m of the equatorial Pacific during January, with areas of cooler than average water between 100 and 200 m depth, extending across the basin westwards of 100 °W. Warm anomalies are greatest in magnitude, exceeding 2 °C warmer than average, in the far eastern Pacific between 130°W and 110°W. Cool anomalies reached more than 2 °C cooler than average across much of their extent.

Warm anomalies have persisted in the central and eastern Pacific between the surface and 200 m depth during October to December 2023. The depth of these warm anomalies has slowly decreased over this period, and extend to only around 100 m depth during January. The magnitude and extent of cool anomalies has also increased across the past few months, and has spread eastwards. This sub-surface pattern of a layer of warmer than average waters above a layer of cooler than average waters is typical of the declining phase of El Niño.

For the 5 days ending 18 February 2024, sub-surface temperatures were more than 2 °C warmer than average across the top 50 m of the equatorial Pacific east of 130°W. Elsewhere, anomalies in the western and central Pacific were generally within 1 °C of average. An area of cool anomalies, reaching more than 2 °C cooler than average, was present between 50 and 150 m depth in the eastern equatorial Pacific between 115°W and 130°W.

Compared to last fortnight, the magnitude of warm anomalies in the central and eastern Pacific has decreased, while the area of cool anomalies below 50 m has continued to move eastwards and towards the surface.

El Niño persists, although a steady weakening trend is evident in the oceanic indicators. Sea surface temperatures in the central tropical Pacific and temperatures in the Pacific sub-surface show a clear cooling trend, in line with typical event decay. Atmospheric indicators have been mixed over the past fortnight; cloudiness near the Date Line has increased, while the 30-day Southern Oscillation Index (SOI) has returned to negative values (both characteristic of an El Niño state). This is expected to be a temporary fluctuation (often observed during summer) and most likely the result of the slow-moving Madden Julian Oscillation in the region.

International climate models suggest the central tropical Pacific Ocean will continue to cool in the coming months, with four of seven climate models indicating the central Pacific is likely to return to neutral El Niño–Southern Oscillation (ENSO) levels in April (i.e., neither El Niño nor La Niña), and all models neutral in May. ENSO predictions made in late summer and autumn tend to have lower accuracy than predictions made at other times of the year. This means that current forecasts of the ENSO state beyond May should be used with caution.

Based on the historical record from 1900, around 50% of El Niño events have been followed by a neutral year, and 40–50% have been followed by La Niña. However, global oceans have warmed significantly over the past 50 years. The oceans have been the warmest on record globally between April 2023 and January 2024. These changes may make a difference when predicting future ENSO events based on historical activity.

The Indian Ocean Dipole (IOD) is neutral. The majority of model forecasts indicate the IOD will be neutral until at least April, consistent with the annual cycle of the IOD.

The Southern Annular Mode (SAM) index is currently positive as at 17 February. Forecasts indicate the SAM index will fall briefly to negative SAM levels over the coming week, and then back to neutral SAM levels for the remainder of the coming fortnight. Neutral SAM has little influence on Australian rainfall patterns.

The Madden–Julian Oscillation (MJO) has weakened significantly in the central Pacific Ocean in the past week and is now weak or indiscernible.  All international climate models indicate the MJO will remain weak in the coming week, with some models suggesting a strengthening in Maritime Continent at the start of March.

The global mean temperature for the 12 months February 2023 to January 2024 was the highest on record, with Copernicus reporting that it was 1.52 °C above the 1850–1900 pre-industrial average. However, the magnitude of global warming is assessed using multi-year averages, and a single 12-month period does not mean that the 1.5 °C target referred to in the Paris Agreement has been exceeded.

Australia's climate has warmed by 1.50 ± 0.23 °C between 1910 and 2023, leading to an increase in the frequency of extreme heat events. In recent decades, there has also been a trend towards a greater proportion of rainfall from high intensity, short duration rainfall events, especially across northern Australia during the wet season. April to October rainfall has declined across southern Australia in recent decades, due to a combination of long-term natural variability and changes in atmospheric circulation caused by increasing greenhouse gas concentrations.

The Southern Annular Mode (SAM) index is currently positive as at 17 February 2024. Forecasts indicate the SAM index will fall briefly to negative SAM values over the coming week, before returning to neutral SAM values for the remainder of the coming fortnight. A neutral SAM has little influence on Australian rainfall patterns.

International model forecasts indicate cooling of the central and eastern equatorial Pacific is likely over the coming months. Sea surface temperatures in the tropical Pacific are expected to return to neutral levels (neither El Niño nor La Niña) in the southern hemisphere autumn 2024, with four of seven climate models indicating the central Pacific is likely to return to neutral ENSO levels in April, and all models neutral in May.

By July, five of seven climate models remain neutral, with two models suggesting cooling to La Niña levels is possible. However, ENSO predictions made in late summer and early autumn tend to have lower accuracy than predictions made at other times of the year. This means that current forecasts of the ENSO state beyond May should be used with caution.

Product code: IDCKGEWW00

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