Australia's incoming deluge: 'Strong odds' of significantly wetter than usual weather in the NT, Queensland as Pacific Ocean gives clues that La Nina could return
The year so far has been marked by rain and floods in the east and drought in the south, with wet weather now suddenly picking up in the drought-stricken southern growing regions that need it most.
Now, this Sky News Weather climate analysis can reveal that many more rain-bearing systems are on the way. Indian Ocean
Avid weather watchers will no doubt be aware that there is plenty of talk about a negative phase of the Indian Ocean Dipole (-IOD) developing and aiding rainfall across Australia.
The Indian Ocean lies to Australia's west.
It is currently in a neutral state with the IOD sitting at -0.04C.
This value needs to fall below -0.4C for at least eight consecutive weeks for these developments to be declared a -IOD event.
It's still a long way off, but forecast models have been in strong agreement for some time that an event is a significant chance to take place.
Its influence could be noticeable from as early as late August if it drops below the threshold in the coming weeks. Pacific Ocean
The ocean to our east is the largest in the world – covering more than 30 per cent of the world's surface.
Its size and proximity have contributed to its outsized influence on our weather.
This mass expanse of water has played a significant role in helping the last five financial years exceed the nation's median rainfall.
We had three back-to-back La Ninas, then an El Nino then a 'La Nina-like' pattern that was declared by Sky News Weather and US Government's climate organisation NOAA, but not by the Bureau of Meteorology.
Right now, the official value of the Nino3.4 index is –0.14C.
However, when comparing the temperatures in the middle of the Pacific Ocean to those through the rest of the world's tropics we can see that we are more clearly on the La Nina side of neutral.
The Relative NINO index is therefore more appropriate to use in a changing climate – currently sitting closer to –0.4C.
Forecast models have suddenly come into line agreeing that significant cooling of the central Pacific is likely.
Between July and September, the median of nine leading models cools the NINO region by between 0.2C and 0.7C with an average of 0.45C.
Therefore, there is a significant chance that the September value of the Relative NINO index will be close to -0.8C.
This puts us on the border of a weak La Nina event.
But like last year, even if it cools a bit further than that, the Bureau will probably say we are experiencing 'La Nina-like conditions' without declaring an event - as official thresholds are unlikely to be met. Rain odds increasing for most
According to the average of the nine aforementioned models – including the Bureau's – there is between a 60 per cent and 90 per cent chance of above median rainfall across Australia from August to October.
This is a notable increase on the previous forecast for the same period – indicating the growing confidence in the upcoming rainfall pattern.
The odds are strongest in the NT and Queensland – meaning that parts of the dry season and 'build-up' months could be significantly wetter than usual – but this is still nothing compared to the wet season.
Further south, rainfall should also be very handy in drought affected regions of SA, Victoria and possibly Tasmania and Western Australia – although their rain chances are not quite as high.
Many farmers will remember the last time we had strong rain odds at this time of year.
Rain gradually picked up through the winter of 2022 before the country saw its second wettest spring on record.
Forbes experienced near-record flooding and the Murray had its biggest flood since 1956.
Models are not quite as extreme in their forecasts this year as they were in the lead up to that event.
However, similar rainfall patterns cannot be ruled out through the coming months as evidenced by this week's uptick in wet weather. Sydney and the NSW coastline could miss out
Sydney and the NSW coast have been pretty wet this year.
Historically the first half of the year is the wetter time of year in these areas.
It's therefore unlikely that the second half of the year will be wetter than the first half.
Further to that – a lot of the upcoming rainfall is expected to favour the NSW ranges and areas further west.
Therefore, it seems likely that rainfall in Sydney and up and down the NSW coast should be somewhat closer to normal.
Locals in those areas may not notice the drenching affecting much of the country.
Watch Sky News Weather on the Sky News App or on Foxtel's Channel 601 for the latest forecasts and seasonal outlooks.
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7NEWS
16 hours ago
- 7NEWS
Rain intensifies in both Queensland, NSW and the west as we head into the weekend
There are two major weather systems brewing - one on either side of the country. Let's start with the eastern one, which will be another significant rain system for Queensland, particularly in the southeast near the coast. If you are in between Brisbane and Mackay, please keep up to date with the latest forecasts and warnings, as a low develops off the coast, fed by tropical moisture, resulting in heavy rain. The rain should start to spread across much of Queensland and northern NSW during the day on Friday. A nice drop from this one, rather than widespread intense rain. The activity intensifies on Saturday along the coast with modelling suggesting widespread falls of 25mm to 100mm. Locally up to 300mm in the most affected area near the low, which is currently between Maryborough and Yeppoon. This one is relatively fast though, with the weather rapidly easing again on Sunday. High pressure brings a dry weekend to the southeast, but in the west of the country we have the next big system move through. Again this will have a good feed of moisture from the tropics - the Indian Ocean - ensuring that the rainband that moves through with the gusty cold front is moisture-laden and brings 25mm to 50mm to the southwest corner, before slowly decreasing as you head inland. This is a strong cold front, and will be accompanied by the usual wind threats. Most of this is felt later Saturday into Sunday. These are ongoing examples of weather systems meeting up with tropical moisture to bring heavier than usual rain for those in the path of the low, trough or front. The global patterns in both the Indian and Pacific Oceans tell us when this injection of moisture is more likely - when we are in a Negative Indian Ocean Dipole (IOD) or a La Nina. Put simply, a Negative IOD is the Indian Ocean equivalent of La Nina, just without the fancy name. They both act to push extra moisture towards Australia. We crossed the threshold into a Negative IOD about a week and a half ago, and remain there this week. Most forecasts have us remaining below that threshold for the next month or two. If we remain there for about eight weeks in total it will officially be a Negative IOD. The Pacific Ocean has weak signs of heading towards that negative threshold too - ie a La Nina. It is one to watch to see if we have both oceans enhancing our moisture over the next few months. It won't ensure rain for all though - only those in the path of the lows.
ABC News
a day ago
- ABC News
Wet weather forecast for spring as Indian Ocean climate driver emerges
A wet finish to the year is increasingly favoured across Australia as a major climate driver emerges for the first time in three years. During recent weeks, changes in ocean temperatures show the development of a negative Indian Ocean Dipole (IOD) — the wet phase of the Indian Ocean, which rivals La Niña for its positive impact on Australia's rainfall. Negative IODs in the past have contributed to most of Australia's wettest winters and springs on record, including all four previous episodes this century in 2010, 2016, 2021 and 2022. A negative IOD refers to a prolonged period of at least eight weeks of warmer waters near Indonesia and cooler waters off the Horn of Africa. While this may seem inconsequential, the change corresponds with a shift in the overlying pressure and wind regime — specifically, there is a moist air blowing towards Australia's longitudes from the tropical Indian Ocean. In a similar vein to a La Niña phase of the Pacific Ocean, this influx of humid winds promotes the formation of cloud and rain. What is critical for the continued evolution of an event and its eventual impact on the weather is that the changes to the ocean and atmosphere reinforce each other through a positive feedback loop — a coupling that can preserve the anomalous state for months. Negative IODs, and their counterpart positive IODs, on average occur every one in five years. However, the Indian Ocean has been exceptionally active during the past decade, with only three years (2017, 2002 and 2024) remaining neutral. The prospect of a negative IOD returning in 2025 was first flagged by the Bureau of Meteorology (BOM) back in autumn when their long-range modelling was showing the driver would likely develop at some point in winter. Despite little observational verification, the BOM's modelling consistently stuck to that prediction through June. However, water temperatures off the east coast of Africa began to drop notably in July. The index used to measure the state of the Indian Ocean reflected this change, and its latest weekly value sits at -0.6 degrees Celsius, below the negative IOD threshold of -0.4°C for the second consecutive week. However, for 2025 to officially become a negative IOD year, the index is required to remain below -0.4°C for at least another six weeks. That scenario now appears increasingly likely with the latest modelling showing the index falling to around -1°C in September before gradually climbing back to neutral in December, easily sufficient time to have a lasting impression on the nation's weather. The BOM's modelling shows negative IOD conditions will intensify further into early spring and remain until December. The life span of an IOD event is shorter than Pacific El Niño-La Niña episodes, which normally last about nine months. A typical IOD will develop in winter, quickly peak, then decay by early summer when the monsoon erodes any influence on tropical Indian Ocean winds. The impacts, shown in the table below, are most pronounced in spring when the national average rainfall is on average 36 per cent higher than during neutral years, calculated using 13 negative IOD events from 1960 to 2024. Winter sees an average 20 per cent boost to precipitation, and by summer it falls to 13.9 per cent. In terms of spatial extent, negative IODs can lift rainfall across most of the country, as illustrated by the map below. The greatest impact lies over the south-east inland where the mean across nine classic events is in the ninth decile — rainfall totals in the top 20 per cent of all years. However, not all events are the same, and considering many negative IODs coincide with La Niña, 2025 rainfall may not be as widespread or intense. So what can we expect during the coming months? The most accurate forecast for seasonal weather patterns is now model data, as opposed to the old method, a few decades ago, of using past years as a guide. The BOM's latest outlook for spring shows a 70 to 80 per cent chance of above-median rain across most of central and eastern Australia, a forecast closely matching a typical negative IOD footprint. Another impact of a negative IOD is on temperatures. Climate change ensures most Australian seasons are comfortably warmer than normal, however, during extended wet periods, the additional cloud cover can lower daytime temperatures. Again, the seasonal outlook concurs with this past trend, showing parts of Australia's central and eastern areas are favoured to record below-median maximums from August to November.
Sky News AU
27-07-2025
- Sky News AU
Australia's incoming deluge: 'Strong odds' of significantly wetter than usual weather in the NT, Queensland as Pacific Ocean gives clues that La Nina could return
There are strong odds of Australia's late winter and spring months being wetter than usual - and significantly so in the NT and Queensland - with Pacific Ocean indicators pointing to a potential La Nina event in 2025. The year so far has been marked by rain and floods in the east and drought in the south, with wet weather now suddenly picking up in the drought-stricken southern growing regions that need it most. Now, this Sky News Weather climate analysis can reveal that many more rain-bearing systems are on the way. Indian Ocean Avid weather watchers will no doubt be aware that there is plenty of talk about a negative phase of the Indian Ocean Dipole (-IOD) developing and aiding rainfall across Australia. The Indian Ocean lies to Australia's west. It is currently in a neutral state with the IOD sitting at -0.04C. This value needs to fall below -0.4C for at least eight consecutive weeks for these developments to be declared a -IOD event. It's still a long way off, but forecast models have been in strong agreement for some time that an event is a significant chance to take place. Its influence could be noticeable from as early as late August if it drops below the threshold in the coming weeks. Pacific Ocean The ocean to our east is the largest in the world – covering more than 30 per cent of the world's surface. Its size and proximity have contributed to its outsized influence on our weather. This mass expanse of water has played a significant role in helping the last five financial years exceed the nation's median rainfall. We had three back-to-back La Ninas, then an El Nino then a 'La Nina-like' pattern that was declared by Sky News Weather and US Government's climate organisation NOAA, but not by the Bureau of Meteorology. Right now, the official value of the Nino3.4 index is –0.14C. However, when comparing the temperatures in the middle of the Pacific Ocean to those through the rest of the world's tropics we can see that we are more clearly on the La Nina side of neutral. The Relative NINO index is therefore more appropriate to use in a changing climate – currently sitting closer to –0.4C. Forecast models have suddenly come into line agreeing that significant cooling of the central Pacific is likely. Between July and September, the median of nine leading models cools the NINO region by between 0.2C and 0.7C with an average of 0.45C. Therefore, there is a significant chance that the September value of the Relative NINO index will be close to -0.8C. This puts us on the border of a weak La Nina event. But like last year, even if it cools a bit further than that, the Bureau will probably say we are experiencing 'La Nina-like conditions' without declaring an event - as official thresholds are unlikely to be met. Rain odds increasing for most According to the average of the nine aforementioned models – including the Bureau's – there is between a 60 per cent and 90 per cent chance of above median rainfall across Australia from August to October. This is a notable increase on the previous forecast for the same period – indicating the growing confidence in the upcoming rainfall pattern. The odds are strongest in the NT and Queensland – meaning that parts of the dry season and 'build-up' months could be significantly wetter than usual – but this is still nothing compared to the wet season. Further south, rainfall should also be very handy in drought affected regions of SA, Victoria and possibly Tasmania and Western Australia – although their rain chances are not quite as high. Many farmers will remember the last time we had strong rain odds at this time of year. Rain gradually picked up through the winter of 2022 before the country saw its second wettest spring on record. Forbes experienced near-record flooding and the Murray had its biggest flood since 1956. Models are not quite as extreme in their forecasts this year as they were in the lead up to that event. However, similar rainfall patterns cannot be ruled out through the coming months as evidenced by this week's uptick in wet weather. Sydney and the NSW coastline could miss out Sydney and the NSW coast have been pretty wet this year. Historically the first half of the year is the wetter time of year in these areas. It's therefore unlikely that the second half of the year will be wetter than the first half. Further to that – a lot of the upcoming rainfall is expected to favour the NSW ranges and areas further west. Therefore, it seems likely that rainfall in Sydney and up and down the NSW coast should be somewhat closer to normal. Locals in those areas may not notice the drenching affecting much of the country. Watch Sky News Weather on the Sky News App or on Foxtel's Channel 601 for the latest forecasts and seasonal outlooks.
