October precipitation outlook for Australia
By
Jason Nicholls, AccuWeather senior meteorologist
Published Sep 24, 2020 1:49 PM EDT
Looking back at rainfall over the past 30 days, we can see some rainfall deficits across eastern Australia and a large dry area over northwestern Australia. Rainfall over the past week or two has been more favorable across southern Australia.
Now that NOAA has declared a La Nina and the Australia BOM has a La Nina Alert, what does that mean heading deeper into spring? Typically, La Nina conditions tend to be beneficial for rainfall especially across eastern Australia. Another sea-surface based teleconnection is the Indian Ocean Dipole, or IOD, which was record positive in the spring of 2019. The IOD this spring will likely remain neutral to weakly negative. As we can see below when there is a La Nina and -IOD the chance of above-normal rainfall is enhanced in many areas, but this spring we are more likely to have La Nina conditions with minimal, if any, enhancement from the IOD.
The atmospheric component of ENSO, known as the Southern Oscillation Index or SOI, is also an important factor in rainfall across Australia. Usually, the SOI is above +7 with a La Nina and below -7 with El Nino. The SOI has been above the La Nina threshold since August. We expect the SOI will remain at or above the La Nina threshold through spring and well into summer. Below is a look at the latest SOI and a figure showing the correlation with rainfall for each season.
SOI is courtesy of The Long Paddock from the Queensland Government
A couple of shorter-term teleconnections are the MJO or Madden-Julian Oscillation and the Antarctic Oscillation or AAO, also known as SAM or Southern Annular Mode. The MJO is a little tricky to forecast out for long periods and heading into early October it looks to be a weak signal. The AAO, on the other hand, is shown to swing from strongly negative in early October back to positive around mid-month.
AAO forecast courtesy of the CPC
The negative AAO to open October may mean near- to below-normal rainfall across portions of southern Australia early in the month, but signs point to a wetter second half of October in southwestern and eastern Australia.
Many of the latest climate models, shown above, support a wet regime across north-central and eastern Australia. La Nina conditions and a +SOI support this wet idea, but the -AAO and other teleconnections lead us to believe the month of October will begin with near- to below-normal rainfall across southern and eastern Australia. Our rainfall forecast for October, below, does not stray much from most of the climate models. However, we think drier-than-normal conditions will persist over portions of central and northern Western Australia.
For updates and the latest weather forecast in your area, check back to AccuWeather.com, and as a heads-up, the Australian Basin tropical season forecast is due to be released on AccuWeather.com in early October.
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Weather Blogs / Global weather
October precipitation outlook for Australia
By Jason Nicholls, AccuWeather senior meteorologist
Published Sep 24, 2020 1:49 PM EDT
Looking back at rainfall over the past 30 days, we can see some rainfall deficits across eastern Australia and a large dry area over northwestern Australia. Rainfall over the past week or two has been more favorable across southern Australia.
Now that NOAA has declared a La Nina and the Australia BOM has a La Nina Alert, what does that mean heading deeper into spring? Typically, La Nina conditions tend to be beneficial for rainfall especially across eastern Australia. Another sea-surface based teleconnection is the Indian Ocean Dipole, or IOD, which was record positive in the spring of 2019. The IOD this spring will likely remain neutral to weakly negative. As we can see below when there is a La Nina and -IOD the chance of above-normal rainfall is enhanced in many areas, but this spring we are more likely to have La Nina conditions with minimal, if any, enhancement from the IOD.
The atmospheric component of ENSO, known as the Southern Oscillation Index or SOI, is also an important factor in rainfall across Australia. Usually, the SOI is above +7 with a La Nina and below -7 with El Nino. The SOI has been above the La Nina threshold since August. We expect the SOI will remain at or above the La Nina threshold through spring and well into summer. Below is a look at the latest SOI and a figure showing the correlation with rainfall for each season.
SOI is courtesy of The Long Paddock from the Queensland Government
A couple of shorter-term teleconnections are the MJO or Madden-Julian Oscillation and the Antarctic Oscillation or AAO, also known as SAM or Southern Annular Mode. The MJO is a little tricky to forecast out for long periods and heading into early October it looks to be a weak signal. The AAO, on the other hand, is shown to swing from strongly negative in early October back to positive around mid-month.
AAO forecast courtesy of the CPC
The negative AAO to open October may mean near- to below-normal rainfall across portions of southern Australia early in the month, but signs point to a wetter second half of October in southwestern and eastern Australia.
Many of the latest climate models, shown above, support a wet regime across north-central and eastern Australia. La Nina conditions and a +SOI support this wet idea, but the -AAO and other teleconnections lead us to believe the month of October will begin with near- to below-normal rainfall across southern and eastern Australia. Our rainfall forecast for October, below, does not stray much from most of the climate models. However, we think drier-than-normal conditions will persist over portions of central and northern Western Australia.
For updates and the latest weather forecast in your area, check back to AccuWeather.com, and as a heads-up, the Australian Basin tropical season forecast is due to be released on AccuWeather.com in early October.
Report a Typo