Climate Driver Update archive
Climate drivers in the Pacific, Indian and Southern oceans and the Tropics
Average of international model outlooks for NINO3.4
Average of international model outlooks for IOD
Sea surface temperature maps
Sea surface temperature maps are not available for forecasts before Spring 2018
SST outlooks for the next 3 months
ENSO is the oscillation between El Niño and La Niña states in the Pacific region. El Niños typically produce drier seasons, and La Niñas drive wetter years, but the influence of each event varies, particularly in conjunction with other climate influences.
International climate model outlooks
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
Southern Oscillation Index
Cloudiness near the Date Line
The Indian Ocean Dipole (IOD) compares sea surface temperatures. An IOD negative state, having warmer than average sea surface temperatures near Australia, provides more moisture for frontal systems and lows crossing Australia.
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.
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.
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.
The SST map for June 2021 shows SSTs were close to average across most of the equatorial Pacific Ocean, although SSTs over the eastern Pacific Ocean warmed slightly resulting in a small region of warm anomalies off the coast of Ecuador and a reduction of cool anomalies present in May.
SSTs were warmer than average in waters around the west and much of the south of Australia.
June 2021 values of the three key NINO indices were: NINO3 +0.2 °C, NINO3.4 +0.2 °C, and NINO4 +0.2 °C.
Sea surface temperatures (SST) for the tropical Pacific Ocean for the week ending 18 July 2021 were close to average across the equatorial Pacific Ocean.
Warmer than average SSTs continue over the western Pacific Ocean south of the equator, parts of the Maritime Continent, across the Tasman Sea, and around the coast of northern and eastern Australia.
All three NINO indices are within the ENSO-neutral range. The latest values of the three NINO indices in the tropical Pacific for the week ending 18 July 2021 were: NINO3 +0.2 °C, NINO3.4 0.0 °C, and NINO4 +0.1 °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-day Southern Oscillation Index (SOI) for the 30 days ending 18 July was +13.9. The 90-day SOI value was +6.6.
The 30-day value has increased over the past few weeks, resulting from local variations in surface pressure with positive pressure anomalies at Tahiti and negative anomalies at Darwin. The SOI is expected to remain positive in the coming fortnight as a result of these local pressure variations.
Sustained negative values of the SOI below −7 typically indicate El Niño while sustained positive values above +7 typically indicate La Niña. Values between +7 and −7 generally indicate neutral conditions.
Trade winds for the 5 days ending 18 July were stronger than average across the western half of the tropical Pacific.
During El Niño there is a sustained weakening, or even reversal, of the trade winds across much of the tropical Pacific. Conversely, during La Niña, there is a sustained strengthening of the trade winds.
The Madden–Julian Oscillation (MJO) is currently active over the Maritime Continent, and is expected to remain at moderate strength as it progresses eastwards across the Pacific Ocean during the remainder of July, reaching Africa at the start of August.
While over the Maritime Continent and Western Pacific the MJO can strengthen westerly wind anomalies over the Indian Ocean, reinforcing the negative IOD.
A negative IOD event has become established.
The latest weekly value of the Indian Ocean Dipole (IOD) index to 18 July was −0.62 °C. The IOD index has been below the negative IOD threshold (−0.4 °C) for eight of the past nine weeks.
Four of the five international climate models surveyed by the Bureau anticipate the IOD index will remain within negative thresholds until at least mid-spring, with four of five models having returned to neutral values by December.
Weekly sea surface temperatures (SSTs) in the Indian Ocean were warmer than average across much of the eastern half of the basin and parts of the north of the Arabian Sea. SSTs around the Horn of Africa and the Arabian Peninsula have cooled again, with cool anomalies re-emerging close to the coastline.
A negative IOD, and a warmer eastern Indian Ocean generally, increase the chances of above average winter–spring rainfall for parts of southern Australia. Negative IOD also makes below average maximum temperatures more likely across southern Australia, while maximum and minimum temperatures are more likely to be above average for the northern tropics of Australia.
Cloudiness near the Date Line has generally been slightly below average (positive OLR anomalies) during June and July to date.
Equatorial cloudiness near the Date Line typically increases during El Niño (negative OLR anomalies) and decreases during La Niña (positive OLR anomalies).
The four-month sequence of equatorial Pacific sub-surface temperature anomalies (to June) shows a pattern consistent with a neutral ENSO state. Weak warm anomalies were present across much of the column depth from the Date Line westwards, and also close to the surface in the top 100 m depth east of 140°W.
For the five days ending 18 July, sub-surface temperatures were close to average across most of the equatorial Pacific. Anomalies remain similar to two weeks ago and are consistent with an ENSO neutral state.
A negative Indian Ocean Dipole (IOD) is underway. A negative IOD increases the likelihood of above average winter–spring rainfall for much of southern and eastern Australia. Maximum temperatures are also more likely to be below average across southern Australia, while maximum and minimum temperatures are more likely to be above average for the northern tropics of Australia.
The most recent weekly IOD index value is −0.62 °C, with the IOD index having been below the negative IOD threshold for eight of the past nine weeks. Most climate models surveyed by the Bureau predict a negative IOD pattern is likely to persist until at least mid-spring.
The El Niño–Southern Oscillation (ENSO) remains neutral with most oceanic and atmospheric indicators within the neutral range. The past fortnight has seen the Southern Oscillation Index (SOI) increase to +13.9 for the 30 days ending 18 July 2021, although this is mostly due to local sea surface pressure variations at Darwin and Tahiti. Additionally, trade winds are stronger than average in the western half of the Pacific, which may encourage some temporary cooling of the ocean surface. Most climate model outlooks indicate the central tropical Pacific Ocean is likely to cool over the coming months, with three of seven models surveyed by the Bureau indicating this cooling will be enough to reach La Niña thresholds in spring, with the remaining four models staying neutral. This forecast cooling may also be contributing to the outlook for above median rainfall for much of Australia in the coming months.
The Southern Annular Mode (SAM) index is neutral and is forecast to remain neutral for at least the next fortnight. A neutral SAM has little influence on Australian climate.
The Madden–Julian Oscillation (MJO) has recently strengthened over the Maritime Continent, to Australia's north. Most climate models indicate the MJO will continue moving eastwards into the western Pacific over the coming week. An MJO in these regions typically leads to stronger westerly winds over the Indian Ocean, which can reinforce the negative IOD.
Climate change continues to influence Australian and global climate. Australia's climate has warmed by 1.44 ± 0.24 °C over 1910–2019, while southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades.
The Southern Annular Mode (SAM) index is currently neutral, and is expected to remain neutral over the next two weeks.
A neutral SAM has little influence on Australian climate.
The El Niño–Southern Oscillation (ENSO) is currently neutral. Most of the international climate models surveyed by the Bureau anticipate NINO3.4 will cool during the coming months, but vary in how much cooling they expect. Three of the seven surveyed models anticipate NINO3.4 will meet or exceed La Niña thresholds between September and December. The remaining four models predict a neutral ENSO pattern to continue through to the end of 2021.
La Niña typically enhances spring rainfall in eastern Australia, and the shift towards cooler forecast values of NINO3.4 may be contributing to the wetter than average rainfall outlooks for parts of the country.
Product code: IDCKGEWW00