Climate Outlook

3-month climate outlook with rainfall and temperature forecast charts for Australia

Australia should experience summer without the influence of major climate drivers like La Ni&ntilde;a or a negative Indian Ocean Dipole, potentially heightening the risk of heatwaves, extreme heat and bushfires across parts of the country.
<h2>Pacific Ocean climate driver</h2>
During much of 2024, the sea surface temperatures across the central and eastern Pacific have been cooler than average, hinting at a potential La Ni&ntilde;a developing in 2024.
<img src="https://news-images.weatherzone.com.au/twc/ssta.daily.current.png" alt="" width="1787" height="1054" />
Image: Sea surface temperature anomalies in the Pacific Ocean on December 1, 2024. The map shows a classic La Ni&ntilde;a-like pattern, with cooler-than-average water in the central and eastern equatorial Pacific Ocean. Source: NOAA.
La Ni&ntilde;a is a broad-scale circulation in the Pacific Ocean that is characterised by warmer-than-average sea surface temperatures to the northeast of Australia and abnormally cool water in the central and eastern equatorial Pacific Ocean.
The image above shows a pattern like this which is why the Bureau issued a La Ni&ntilde;a Watch earlier this year, meaning that there is a 50% chance of a La Ni&ntilde;a developing this year, or about twice the normal likelihood.
If La Ni&ntilde;a was to occur this summer, it could typically cause:
<ul>
<li>Increased rainfall across much of Australia</li>
<li>Milder daytime temperatures</li>
<li>Warmer nighttime temperatures in the north</li>
<li>Greater risk of Tropical Cyclones</li>
<li>Earlier onset to the monsoon</li>
<li>Increased risk of heatwaves, but at a lower intensity</li>
<li>Increased humidity</li>
</ul>
La Ni&ntilde;a is one of three phases of the El Ni&ntilde;o-Southern Oscillation, with the other two phases being El Ni&ntilde;o and neutral (neither La Ni&ntilde;a nor El Ni&ntilde;o).
We have entered summer in a neutral phase of the El Ni&ntilde;o-Southern Oscillation, which usually brings &lsquo;normal&rsquo; summer weather to Australia.
Recent observations of the Nino 3.4 index show that the Sea Surface Temperatures anomalies in the central equatorial pacific have moved away from the La Nina threshold of -0.8&ordm;C and toward the neutral phase.
<img src="https://news-images.weatherzone.com.au/twc/Nino3.4%20SST%20Index%20(1).png" alt="" width="1920" height="1080" />
Image: Nino3.4 index observations during the last few years.
Both the Ni&ntilde;o 3.4 or 3 indices have not yet met the Bureau&rsquo;s criteria for declaring La Ni&ntilde;a. However, this is not the only criteria used by the Bureau and any three of the following criteria can be used to declare La Ni&ntilde;a:
<ul>
<li>Ni&ntilde;o 3.4 and 3 indices below -0.8&deg;C</li>
<li>Trade winds in the central or western Pacific Ocean stronger than average during any three of the last four months</li>
<li>Southern Oscillation Index (SOI) is +7 or higher for a three-month average.</li>
<li>Majority of models show sustained values below -0.8&deg;C for the Nino3 and Nino3.4 regions</li>
</ul>
Currently only one of these criteria has been met, with stronger trade winds occurring across the western Pacific. The three-month SOI index is 3.7, which is well within neutral boundaries and is unlikely to make this criterion in at least the next three months.
The majority of climate models are predicting neutral conditions this summer. Only two out of the seven models surveyed by the Bureau of Meteorology are predicting La Ni&ntilde;a for December, as shown below.
<img src="https://news-images.weatherzone.com.au/twc/december%20la%20nina.png" alt="" width="650" height="400" />
Image: Global climate model Ni&ntilde;o3.4 index forecasts for December 2024. Source: Bureau of Meteorology.
While the Bureau is unlikely to declare La Ni&ntilde;a this summer, the US Climate Prediction Centre (CPC) and Columbia University&rsquo;s International Research Institute for Climate and Society (IRI) predict that there is a 74% chance of the La Ni&ntilde;a phase of the climate driver emerging this year. However, their La Ni&ntilde;a threshold for the Nino 3.4 index of -0.5&deg;C is less extreme than the Bureau&rsquo;s which is -0.8&deg;C, and therefore easier to meet.
Regardless of the Bureau&rsquo;s declaration, Australia could see La Ni&ntilde;a-like conditions develop during early to mid-summer increasing the chance of rainfall across northern and eastern Australia.
<h2>Indian Ocean climate driver</h2>
Another major climate driver for Australia is the Indian Ocean Dipole (IOD), which is an index that measures the difference in sea surface temperatures across the tropical Indian Ocean.
A negative IOD occurs when cooler-than-average water sits on the western side of the Indian Ocean, near the Horn of Africa, and warmer-than-average water lies on the eastern side of the Indian Ocean, near Indonesia. A positive IOD is the opposite of this pattern (cooler water in the east, warmer in the west).
Each phase of the IOD also influences atmospheric conditions above the Indian Ocean and surrounding countries. For Australia, a negative IOD typically increases the likelihood of above average rain over large areas of the country, while also promoting cooler days in the country&rsquo;s south and east.
IOD events typically occur between May and November and break down when the monsoon arrives in summer.
The IOD index had been in a predominantly negative phase over the last couple of months, since mid-October, however it has recently jumped back into neutral conditions.
<img src="https://news-images.weatherzone.com.au/twc/IOD%20Index.png" alt="" width="1920" height="1080" />
Image: IOD index observations during the last few years.
While it had been negative for weeks, the Bureau typically does not declare a negative IOD event unless the index is below the -0.4&deg;C threshold for at least eight weeks.
While the IOD has been officially neutral and will continue to be with the arrival of the monsoon expected in December, the brief negative phase seen in recent weeks has been causing above average rainfall and storm activity across large areas of Australia.
<img src="https://news-images.weatherzone.com.au/twc/november%20rainfall.png" alt="" width="680" height="468" />
Image: Australian rainfall deciles for November 2024. Source: Bureau of Meteorology
The rainfall in November and also the opening days of December most likely has been caused in part by this negative IOD-like pattern, which is associated with much warmer than average Sea Surface Temperatures (SSTs) off the northwest shelf of Australia.
<img src="https://news-images.weatherzone.com.au/twc/sst_anom_aus_dec1_2024.png" alt="" width="640" height="528" />
Image: Sea surface temperature anomaly for Sunday, December 1. Source Bureau of Meteorology
The unusually warm waters to the northwest of WA are enhancing the moisture in the atmosphere in the region, which is being transported towards the countries southeast by frequent northwest cloud bands.
While the IOD is expected to be neutral in the coming months, these warm waters could continue to enhance rainfall across parts of Australia this summer.
The ocean temperatures to the country's southeast are also abnormally warm, which could increase the potential for rain, thunderstorms and humidity over eastern Australia in the coming months.
Eastern Australia could also see enhanced easterly winds this summer thanks to prolonged phases of positive SAM. This may enhance rain and storm activity in the country&rsquo;s east and southeast in the months ahead.
<h2>What to expect this summer</h2>
During early December, large parts of the country are forecast to be wetter than average due to the warm SSTs surrounding much of Australia, along with the influence of La Ni&ntilde;a-like conditions and the likely arrival of the monsoon.
<img src="https://news-images.weatherzone.com.au/twc/chance%20of%20wetter%20than%20normal%20dec.jpg" alt="" width="1280" height="720" />
<img src="https://news-images.weatherzone.com.au/twc/chance%20of%20wetter%20than%20normal%20jan.jpg" alt="" width="1280" height="720" />
<img src="https://news-images.weatherzone.com.au/twc/febwetterthannormal.jpg" alt="" width="1280" height="720" />
Images: Chance of wetter than normal forecast for the summer months according to the ECMWF-SEAS5 model
You can see in the maps above that later in summer, much of Australia is forecast to become drier than average, except for pockets of eastern Australia.
Despite the rainfall signal in early summer, daytime and nighttime temperatures are forecast to be warmer than average across the country.
With La Ni&ntilde;a and the negative IOD unlikely to occur, Australia faces an increased risk of extreme heat and bushfires this summer.
Large areas of the NT, Vic and parts of NSW, WA and SA have an increased risk of bushfires this summer, with dry and warm conditions forecast to continue.


Australia should experience summer without the influence of major climate drivers like La Niña or a negative Indian Ocean Dipole, potentially heightening the risk of heatwaves, extreme heat and bushfires across parts of the country.


Pacific Ocean climate driver


During much of 2024, the sea surface temperatures across the central and eastern Pacific have been cooler than average, hinting at a potential La Niña developing in 2024.





Image: Sea surface temperature anomalies in the Pacific Ocean on December 1, 2024. The map shows a classic La Niña-like pattern, with cooler-than-average water in the central and eastern equatorial Pacific Ocean. Source: NOAA.


La Niña is a broad-scale circulation in the Pacific Ocean that is characterised by warmer-than-average sea surface temperatures to the northeast of Australia and abnormally cool water in the central and eastern equatorial Pacific Ocean.


The image above shows a pattern like this which is why the Bureau issued a La Niña Watch earlier this year, meaning that there is a 50% chance of a La Niña developing this year, or about twice the normal likelihood.


If La Niña was to occur this summer, it could typically cause:




Increased rainfall across much of Australia


Milder daytime temperatures


Warmer nighttime temperatures in the north


Greater risk of Tropical Cyclones


Earlier onset to the monsoon


Increased risk of heatwaves, but at a lower intensity


Increased humidity




La Niña is one of three phases of the El Niño-Southern Oscillation, with the other two phases being El Niño and neutral (neither La Niña nor El Niño).


We have entered summer in a neutral phase of the El Niño-Southern Oscillation, which usually brings ‘normal’ summer weather to Australia.


Recent observations of the Nino 3.4 index show that the Sea Surface Temperatures anomalies in the central equatorial pacific have moved away from the La Nina threshold of -0.8ºC and toward the neutral phase.





Image: Nino3.4 index observations during the last few years.


Both the Niño 3.4 or 3 indices have not yet met the Bureau’s criteria for declaring La Niña. However, this is not the only criteria used by the Bureau and any three of the following criteria can be used to declare La Niña:




Niño 3.4 and 3 indices below -0.8°C


Trade winds in the central or western Pacific Ocean stronger than average during any three of the last four months


Southern Oscillation Index (SOI) is +7 or higher for a three-month average.


Majority of models show sustained values below -0.8°C for the Nino3 and Nino3.4 regions




Currently only one of these criteria has been met, with stronger trade winds occurring across the western Pacific. The three-month SOI index is 3.7, which is well within neutral boundaries and is unlikely to make this criterion in at least the next three months.


The majority of climate models are predicting neutral conditions this summer. Only two out of the seven models surveyed by the Bureau of Meteorology are predicting La Niña for December, as shown below.





Image: Global climate model Niño3.4 index forecasts for December 2024. Source: Bureau of Meteorology.


While the Bureau is unlikely to declare La Niña this summer, the US Climate Prediction Centre (CPC) and Columbia University’s International Research Institute for Climate and Society (IRI) predict that there is a 74% chance of the La Niña phase of the climate driver emerging this year. However, their La Niña threshold for the Nino 3.4 index of -0.5°C is less extreme than the Bureau’s which is -0.8°C, and therefore easier to meet.


Regardless of the Bureau’s declaration, Australia could see La Niña-like conditions develop during early to mid-summer increasing the chance of rainfall across northern and eastern Australia.


Indian Ocean climate driver


Another major climate driver for Australia is the Indian Ocean Dipole (IOD), which is an index that measures the difference in sea surface temperatures across the tropical Indian Ocean.


A negative IOD occurs when cooler-than-average water sits on the western side of the Indian Ocean, near the Horn of Africa, and warmer-than-average water lies on the eastern side of the Indian Ocean, near Indonesia. A positive IOD is the opposite of this pattern (cooler water in the east, warmer in the west).


Each phase of the IOD also influences atmospheric conditions above the Indian Ocean and surrounding countries. For Australia, a negative IOD typically increases the likelihood of above average rain over large areas of the country, while also promoting cooler days in the country’s south and east.


IOD events typically occur between May and November and break down when the monsoon arrives in summer.


The IOD index had been in a predominantly negative phase over the last couple of months, since mid-October, however it has recently jumped back into neutral conditions.





Image: IOD index observations during the last few years.


While it had been negative for weeks, the Bureau typically does not declare a negative IOD event unless the index is below the -0.4°C threshold for at least eight weeks.


While the IOD has been officially neutral and will continue to be with the arrival of the monsoon expected in December, the brief negative phase seen in recent weeks has been causing above average rainfall and storm activity across large areas of Australia.





Image: Australian rainfall deciles for November 2024. Source: Bureau of Meteorology


The rainfall in November and also the opening days of December most likely has been caused in part by this negative IOD-like pattern, which is associated with much warmer than average Sea Surface Temperatures (SSTs) off the northwest shelf of Australia.





Image: Sea surface temperature anomaly for Sunday, December 1. Source Bureau of Meteorology


The unusually warm waters to the northwest of WA are enhancing the moisture in the atmosphere in the region, which is being transported towards the countries southeast by frequent northwest cloud bands.


While the IOD is expected to be neutral in the coming months, these warm waters could continue to enhance rainfall across parts of Australia this summer.


The ocean temperatures to the country's southeast are also abnormally warm, which could increase the potential for rain, thunderstorms and humidity over eastern Australia in the coming months.


Eastern Australia could also see enhanced easterly winds this summer thanks to prolonged phases of positive SAM. This may enhance rain and storm activity in the country’s east and southeast in the months ahead.


What to expect this summer


During early December, large parts of the country are forecast to be wetter than average due to the warm SSTs surrounding much of Australia, along with the influence of La Niña-like conditions and the likely arrival of the monsoon.











Images: Chance of wetter than normal forecast for the summer months according to the ECMWF-SEAS5 model


You can see in the maps above that later in summer, much of Australia is forecast to become drier than average, except for pockets of eastern Australia.


Despite the rainfall signal in early summer, daytime and nighttime temperatures are forecast to be warmer than average across the country.


With La Niña and the negative IOD unlikely to occur, Australia faces an increased risk of extreme heat and bushfires this summer.


Large areas of the NT, Vic and parts of NSW, WA and SA have an increased risk of bushfires this summer, with dry and warm conditions forecast to continue.


Australia should experience summer without the influence of major climate drivers like La Niña or a negative Indian Ocean Dipole

La Niña and negative IOD declarations unlikely this summer

Australia recorded its warmest spring on record, with also severe rainfall deficiencies occurring across parts of the country, setting the stage for high fire risk this summer.
The Australasian Fire and Emergency Services Authorities Council (AFAC) released their summer bushfire outlook for 2024 on Thursday, November 28, showing large areas of the NT, Vic and parts of NSW, WA and SA have an increased risk of bushfires this summer.
The red shading on the map below shows areas that have an increased risk of fires over the next three months. The remaining grey areas on the map have a near-normal risk of summer fires, according to the AFAC outlook.
<img class="alignnone wp-image-14572 size-large" src="https://apac.dtn.com/app/uploads/2024/12/aus_summer-2024-1024x724.png" alt="" width="1024" height="724" />
Image: Australian seasonal bushfire outlook for spring 2024. Source: AFAC
The AFAC outlook shows elevated fire danger across five states and territories because of:
<ul>
<li>Forecast above average temperatures</li>
<li>The Bureau has forecast drier conditions in mid to late summer across much of Australia, apart from the east of the country which should continue to be wet.</li>
<li>Severe rainfall deficiencies and drought across parts of southern Australia.</li>
<li>Winter spring rainfall which has led to substantial fuel loads in some areas.</li>
<li><a href="https://www.weatherzone.com.au/news/australia-registers-warmest-spring-on-record/1890153">The warmest spring on record</a> which helped dry out and make materials flammable.</li>
<li>Unburnt areas across southern NT.</li>
</ul>
Severe or serious rainfall deficiencies have been observed in northwest, southwest and far southern WA, southern and southeast SA, western and northeast Vic, southern NSW and the northwest and coastal fringes of Tas in the 15 months leading up to November 2024.
 <img class="alignnone wp-image-14575 size-full" src="https://apac.dtn.com/app/uploads/2024/12/15-monthd-def-1.gif" alt="" width="680" height="468" />
Image: Rainfall deficiencies during the 15-month period between August 1, 2023, and October 31, 2023. Source: BOM
The severe drought in these areas has resulted in large amounts of dry or dead plant material which are very flammable. A lack of autumn and winter spring rainfall was also observed across northeast Vic, the Mornington Peninsula, southwest Gippsland and Greater Melbourne and parts of central NSW, increasing the fire risk in these areas during summer.
Meanwhile normal fire risk is forecast for northern and eastern parts of Australia due to the imminent monsoon arrival in the north and above average rainfall forecast in the east. These areas should still remain vigilant during the summer months, if this wetter-than-average weather does not eventuate, the risk of fires will also be higher than normal.


Australia recorded its warmest spring on record, with also severe rainfall deficiencies occurring across parts of the country, setting the stage for high fire risk this summer.


The Australasian Fire and Emergency Services Authorities Council (AFAC) released their summer bushfire outlook for 2024 on Thursday, November 28, showing large areas of the NT, Vic and parts of NSW, WA and SA have an increased risk of bushfires this summer.


The red shading on the map below shows areas that have an increased risk of fires over the next three months. The remaining grey areas on the map have a near-normal risk of summer fires, according to the AFAC outlook.





Image: Australian seasonal bushfire outlook for spring 2024. Source: AFAC


The AFAC outlook shows elevated fire danger across five states and territories because of:




Forecast above average temperatures


The Bureau has forecast drier conditions in mid to late summer across much of Australia, apart from the east of the country which should continue to be wet.


Severe rainfall deficiencies and drought across parts of southern Australia.


Winter spring rainfall which has led to substantial fuel loads in some areas.


The warmest spring on record which helped dry out and make materials flammable.


Unburnt areas across southern NT.




Severe or serious rainfall deficiencies have been observed in northwest, southwest and far southern WA, southern and southeast SA, western and northeast Vic, southern NSW and the northwest and coastal fringes of Tas in the 15 months leading up to November 2024.


 


Image: Rainfall deficiencies during the 15-month period between August 1, 2023, and October 31, 2023. Source: BOM


The severe drought in these areas has resulted in large amounts of dry or dead plant material which are very flammable. A lack of autumn and winter spring rainfall was also observed across northeast Vic, the Mornington Peninsula, southwest Gippsland and Greater Melbourne and parts of central NSW, increasing the fire risk in these areas during summer.


Meanwhile normal fire risk is forecast for northern and eastern parts of Australia due to the imminent monsoon arrival in the north and above average rainfall forecast in the east. These areas should still remain vigilant during the summer months, if this wetter-than-average weather does not eventuate, the risk of fires will also be higher than normal.


Australia just recorded its warmest spring on record, setting the stage for high fire risk this summer.

Australia faces high fire danger this summer

Australia just had its warmest spring on record with a mean temperature more than 2&deg;C above the long-term average.
The national mean temperature in spring 2024 &ndash; which is the average of 112 weather stations spread out across the country &ndash; was about 24.58&deg;C. This is exceptionally high for spring, coming in at 2.08&deg;C above the 1961-90 long-term average.
This huge anomaly made spring 2024 Australia&rsquo;s warmest spring in records dating back to 1910, beating the previous record of +2.03&deg;C from 2020.
<img src="https://news-images.weatherzone.com.au/twc/spring_meantempgraph_aus_spring2024.png" alt="" width="1280" height="960" />
Image: Australia&rsquo;s spring mean temperature anomalies between 1910 and 2024. Source: Bureau of Meteorology.
Nowhere in Australia had a cooler-than-average spring, and most of the country experienced average spring temperatures that were in the top 10 percent of historical records.
The map below shows the observed mean temperature deciles for Australia in spring 2024. The orange shading shows that temperatures were above average almost everywhere, while the darkest shading reveals that parts of four states and one territory experienced record-breaking warmth during the season.
<img src="https://news-images.weatherzone.com.au/twc/mean_decile_aus_spring2024.gif" alt="" width="680" height="467" />
Image: Observed mean temperature deciles during spring 2024. Source: Bureau of Meteorology
Here&rsquo;s how spring 2024 ranked out of 115 years of observations (1910 to 2024) for each state and territory, based on the mean temperature anomaly relative to 1961-90:
<ul>
<li>Queensland: +2.47&deg;C - warmest on record</li>
<li>WA: +2.02&deg;C - 3rd warmest on record</li>
<li>NSW/ACT: +2.17&deg;C - 8th warmest on record</li>
<li>SA: +2.15&deg;C - 5th warmest on record</li>
<li>NT: +1.70&deg;C - 4th warmest on record</li>
<li>Victoria: +1.60&deg;C - 6th warmest on record</li>
<li>Tasmania: +0.76&deg;C - 9th warmest on record</li>
</ul>
Last season&rsquo;s exceptional air temperature anomaly was partially driven by the influence of abnormally warm oceans surrounding the country. While the final data isn&rsquo;t yet available for the whole season, sea surface temperatures in the Australian region were running at record-breaking levels through the middle of the season and have remained well above average in recent weeks.
<img src="https://news-images.weatherzone.com.au/twc/sst_anom_nov_30.png" alt="" width="1491" height="909" />
Image: Sea surface temperature anomaly on the final day of spring 2024, showing abnormally warm water surrounding Australia. Source: NOAA
Australia&rsquo;s record-breaking spring warmth is one piece of a larger puzzle that reveals a broader picture of global warming in 2024. According to the <a href="https://wmo.int/news/media-centre/2024-track-be-hottest-year-record-warming-temporarily-hits-15degc#:~:text=1.5%C2%B0C-,2024%20is%20on%20track%20to%20be%20hottest%20year%20on%20record,temporarily%20hits%201.5%C2%B0C&amp;text=Baku%2C%20Azerbaijan%20(WMO)%20%2D,World%20Meteorological%20Organization%20(WMO)." target="_blank" rel="noopener">World Meteorological Organization</a>, 2024 is on track to become Earth&rsquo;s hottest year on record.


Australia just had its warmest spring on record with a mean temperature more than 2°C above the long-term average.


The national mean temperature in spring 2024 – which is the average of 112 weather stations spread out across the country – was about 24.58°C. This is exceptionally high for spring, coming in at 2.08°C above the 1961-90 long-term average.


This huge anomaly made spring 2024 Australia’s warmest spring in records dating back to 1910, beating the previous record of +2.03°C from 2020.





Image: Australia’s spring mean temperature anomalies between 1910 and 2024. Source: Bureau of Meteorology.


Nowhere in Australia had a cooler-than-average spring, and most of the country experienced average spring temperatures that were in the top 10 percent of historical records.


The map below shows the observed mean temperature deciles for Australia in spring 2024. The orange shading shows that temperatures were above average almost everywhere, while the darkest shading reveals that parts of four states and one territory experienced record-breaking warmth during the season.





Image: Observed mean temperature deciles during spring 2024. Source: Bureau of Meteorology


Here’s how spring 2024 ranked out of 115 years of observations (1910 to 2024) for each state and territory, based on the mean temperature anomaly relative to 1961-90:




Queensland: +2.47°C - warmest on record


WA: +2.02°C - 3rd warmest on record


NSW/ACT: +2.17°C - 8th warmest on record


SA: +2.15°C - 5th warmest on record


NT: +1.70°C - 4th warmest on record


Victoria: +1.60°C - 6th warmest on record


Tasmania: +0.76°C - 9th warmest on record




Last season’s exceptional air temperature anomaly was partially driven by the influence of abnormally warm oceans surrounding the country. While the final data isn’t yet available for the whole season, sea surface temperatures in the Australian region were running at record-breaking levels through the middle of the season and have remained well above average in recent weeks.





Image: Sea surface temperature anomaly on the final day of spring 2024, showing abnormally warm water surrounding Australia. Source: NOAA


Australia’s record-breaking spring warmth is one piece of a larger puzzle that reveals a broader picture of global warming in 2024. According to the World Meteorological Organization, 2024 is on track to become Earth’s hottest year on record.


Australia just had its warmest spring on record with a mean temperature more than 2°C above the long-term average.


The national mean temperature in spring 20...

Australia registers warmest spring on record

The Southern Annular Mode (SAM) has shifted into a positive phase and Australia is already feeling its wet and stormy influence. With this positive SAM expected to linger into the back half of November, enhanced rain and thunderstorm activity is likely to remain a prominent feature over Australia in the coming weeks.
<h2>What is the Southern Annular Mode?</h2>
The SAM is one of Australia main broad-scale climate drivers. It typically influences Australia&rsquo;s day-to-day weather patterns on the scale of a few weeks at a time.
The SAM is an index that measures the north-south displacement of a westerly wind belt that flows around the middle latitudes Southern Hemisphere, passing between Australia and Antarctica.
When the SAM is in a positive phase, these westerly winds, and the cold fronts and low pressure systems they carry, are located further south than usual for that time of year. When the SAM is negative, the westerly winds, fronts and low are positioned further north than usual for that time of year.
The SAM&rsquo;s influence on Australian weather varies throughout the year. For example, a negative SAM typically increases wind, rain and snow potential over large areas of southern Australia in winter. By contrast, a negative SAM in summer increases the likelihood of dry weather over most of southeastern and eastern Australia.
<h2>What is the SAM doing now?</h2>
The SAM entered a positive phase in the first week of November and has remained positive in the past fortnight. Forecast models suggest that this positive SAM phase should linger throughout November and could spill into early December.
<img src="https://news-images.weatherzone.com.au/twc/sam_index.daily.20241111.png" alt="" width="720" height="480" />
Image: SAM observations and forecast. Source: Bureau of Meteorology
A positive SAM during late spring and early summer usually increases the flow of air from the Coral and Tasman Seas towards eastern Australia. This increase in moisture-laden easterly winds can enhance rain and thunderstorm activity over much of eastern and southeastern Australia.
<img src="https://news-images.weatherzone.com.au/twc/SAM%20Summer%20-%20Positive%20copy_1.jpeg" alt="" width="2500" height="1900" />
Image: Typical positive SAM impacts during summer.
This month&rsquo;s positive SAM event is already having a noticeable impact on Australia&rsquo;s weather, and this influence will likely continue into the back half of November.
Rain and thunderstorms have developed over parts of eastern Australia almost every day this month, with <a href="https://www.weatherzone.com.au/news/severe-storms-striking-eastern-australia-on-wednesday/1890079" target="_blank" rel="noopener">severe thunderstorms</a> hitting parts of Qld and NSW on numerous occasions in the past fortnight.
Looking ahead, computer models predict further wet and stormy weather over large parts of Australia in the coming two weeks, including large areas of eastern Australia.
<img src="https://news-images.weatherzone.com.au/twc/aus_rain_20241114_sqare.png" alt="" width="1080" height="1080" />
Image: Forecast accumulated rain during the next 7 days (for the week ending on Wednesday, November 20, 2024).
The map above shows that eastern Australia is not the only part of the country that&rsquo;s expecting substantial rain in the coming week. In addition to the positive SAM, above average sea surface temperatures to the northwest of Australia will also help fuel widespread rain and thunderstorms over northern and western Australia in the coming fortnight.


The Southern Annular Mode (SAM) has shifted into a positive phase and Australia is already feeling its wet and stormy influence. With this positive SAM expected to linger into the back half of November, enhanced rain and thunderstorm activity is likely to remain a prominent feature over Australia in the coming weeks.


What is the Southern Annular Mode?


The SAM is one of Australia main broad-scale climate drivers. It typically influences Australia’s day-to-day weather patterns on the scale of a few weeks at a time.


The SAM is an index that measures the north-south displacement of a westerly wind belt that flows around the middle latitudes Southern Hemisphere, passing between Australia and Antarctica.


When the SAM is in a positive phase, these westerly winds, and the cold fronts and low pressure systems they carry, are located further south than usual for that time of year. When the SAM is negative, the westerly winds, fronts and low are positioned further north than usual for that time of year.


The SAM’s influence on Australian weather varies throughout the year. For example, a negative SAM typically increases wind, rain and snow potential over large areas of southern Australia in winter. By contrast, a negative SAM in summer increases the likelihood of dry weather over most of southeastern and eastern Australia.


What is the SAM doing now?


The SAM entered a positive phase in the first week of November and has remained positive in the past fortnight. Forecast models suggest that this positive SAM phase should linger throughout November and could spill into early December.





Image: SAM observations and forecast. Source: Bureau of Meteorology


A positive SAM during late spring and early summer usually increases the flow of air from the Coral and Tasman Seas towards eastern Australia. This increase in moisture-laden easterly winds can enhance rain and thunderstorm activity over much of eastern and southeastern Australia.





Image: Typical positive SAM impacts during summer.


This month’s positive SAM event is already having a noticeable impact on Australia’s weather, and this influence will likely continue into the back half of November.


Rain and thunderstorms have developed over parts of eastern Australia almost every day this month, with severe thunderstorms hitting parts of Qld and NSW on numerous occasions in the past fortnight.


Looking ahead, computer models predict further wet and stormy weather over large parts of Australia in the coming two weeks, including large areas of eastern Australia.





Image: Forecast accumulated rain during the next 7 days (for the week ending on Wednesday, November 20, 2024).


The map above shows that eastern Australia is not the only part of the country that’s expecting substantial rain in the coming week. In addition to the positive SAM, above average sea surface temperatures to the northwest of Australia will also help fuel widespread rain and thunderstorms over northern and western Australia in the coming fortnight.


The Southern Annular Mode (SAM) has shifted into a positive phase and Australia is already feeling its wet and stormy influence. With this positive SAM expected...

A positive SAM has arrived – here's what it means for Australian weather

Sea surface temperatures in the Indian Ocean suggest that a negative phase of the Indian Ocean Dipole (IOD) may be emerging, which could influence Australian weather patterns in the coming months.
<h2>What is the Indian Ocean Dipole?</h2>
The IOD is an index that measures the difference in sea surface temperatures across the tropical Indian Ocean. A negative IOD occurs when cooler-than-average water sits on the western side of the Indian Ocean, near the Horn of Africa, and warmer-than-average water lies on the eastern side of the Indian Ocean, near Indonesia. A positive IOD is the opposite of this pattern (cooler water in the east, warmer in the west).
Each phase of the IOD also influences atmospheric conditions above the Indian Ocean and surrounding countries. For Australia, a negative IOD typically increases the likelihood of above average rain over large areas of the country, while also promoting cooler days in the country&rsquo;s south and east.
IOD events typically occur between May and November and break down when the monsoon arrives in late winter or early summer. While October is late in the year for an IOD event to become established, there is still time for a negative IOD this spring. The maps below show how a negative IOD would typically impact Australian weather between October and December.
<img src="https://news-images.weatherzone.com.au/twc/iod_negative_rain_OND.png" alt="" width="675" height="459" />
Image: Typical changes to rainfall when a negative IOD occurs between October and December. Source: Bureau of Meteorology
<img src="https://news-images.weatherzone.com.au/twc/iod_negative_maxtemp_OND.png" alt="" width="675" height="459" />
Image: Typical changes to maximum temperature when a negative IOD occurs between October and December. Source: Bureau of Meteorology
<h2>Negative IOD pattern emerging</h2>
The IOD is currently in a neutral phase, meaning neither a positive nor negative IOD is occurring. However, the map below shows sea surface temperature anomalies in the two IOD monitoring regions are beginning to reflect a negative IOD, with abnormally cool water in the west and warmer-than-average water in the east.
<img src="https://news-images.weatherzone.com.au/twc/iod_sst_20241013.jpg" alt="" width="1333" height="909" />
Image: Sea surface temperature anomalies in the IOD monitoring regions on October 13, 2024. Source: NOAA
In Australia, a negative IOD occurs when we see sustained IOD values below -0.4&deg;C. The latest weekly IOD value was -0.58&deg;C, which is the first reading below the -0.4&deg;C threshold since 2022.
Most forecast models suggest that the IOD index will remain below -0.4&deg;C through the second half of spring before returning to neutral values in December.
<img src="https://news-images.weatherzone.com.au/twc/20241012iod_summary.png" alt="" width="650" height="280" />
Image: IOD outlook for November 2024 from five international forecast models, all showing a weak negative IOD signal lingering through late spring. Source: Bureau of Meteorology.
While it&rsquo;s currently not clear whether a negative IOD will be declared in 2024, current conditions and forecast models are leaning towards Australia experiencing negative IOD-like weather in the second half of spring.
The maps below show predicted rainfall anomalies from the ECMWF-SEAS5 model for November 2024. The first map shows a signal of above average rain over the central and eastern Indian Ocean and below average in the western Indian Ocean. The second map highlights an increased likelihood for rain in northern and eastern Australia during November.
<img src="https://news-images.weatherzone.com.au/twc/seasonal-monthly-precip-anom-global-nov2024.jpg" alt="" width="1920" height="1080" />
Image: Global rainfall anomaly forecast for November 2024.
<img src="https://news-images.weatherzone.com.au/twc/seasonal-monthly-precip-anom-au-nov2024.jpg" alt="" width="1920" height="1080" />
Image: Australian rainfall anomaly forecast for November 2024.


Sea surface temperatures in the Indian Ocean suggest that a negative phase of the Indian Ocean Dipole (IOD) may be emerging, which could influence Australian weather patterns in the coming months.


What is the Indian Ocean Dipole?


The IOD is an index that measures the difference in sea surface temperatures across the tropical Indian Ocean. A negative IOD occurs when cooler-than-average water sits on the western side of the Indian Ocean, near the Horn of Africa, and warmer-than-average water lies on the eastern side of the Indian Ocean, near Indonesia. A positive IOD is the opposite of this pattern (cooler water in the east, warmer in the west).


Each phase of the IOD also influences atmospheric conditions above the Indian Ocean and surrounding countries. For Australia, a negative IOD typically increases the likelihood of above average rain over large areas of the country, while also promoting cooler days in the country’s south and east.


IOD events typically occur between May and November and break down when the monsoon arrives in late winter or early summer. While October is late in the year for an IOD event to become established, there is still time for a negative IOD this spring. The maps below show how a negative IOD would typically impact Australian weather between October and December.





Image: Typical changes to rainfall when a negative IOD occurs between October and December. Source: Bureau of Meteorology





Image: Typical changes to maximum temperature when a negative IOD occurs between October and December. Source: Bureau of Meteorology


Negative IOD pattern emerging


The IOD is currently in a neutral phase, meaning neither a positive nor negative IOD is occurring. However, the map below shows sea surface temperature anomalies in the two IOD monitoring regions are beginning to reflect a negative IOD, with abnormally cool water in the west and warmer-than-average water in the east.





Image: Sea surface temperature anomalies in the IOD monitoring regions on October 13, 2024. Source: NOAA


In Australia, a negative IOD occurs when we see sustained IOD values below -0.4°C. The latest weekly IOD value was -0.58°C, which is the first reading below the -0.4°C threshold since 2022.


Most forecast models suggest that the IOD index will remain below -0.4°C through the second half of spring before returning to neutral values in December.





Image: IOD outlook for November 2024 from five international forecast models, all showing a weak negative IOD signal lingering through late spring. Source: Bureau of Meteorology.


While it’s currently not clear whether a negative IOD will be declared in 2024, current conditions and forecast models are leaning towards Australia experiencing negative IOD-like weather in the second half of spring.


The maps below show predicted rainfall anomalies from the ECMWF-SEAS5 model for November 2024. The first map shows a signal of above average rain over the central and eastern Indian Ocean and below average in the western Indian Ocean. The second map highlights an increased likelihood for rain in northern and eastern Australia during November.





Image: Global rainfall anomaly forecast for November 2024.





Image: Australian rainfall anomaly forecast for November 2024.


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