A Wet Finish to the Year is Increasingly Favoured Across Australia AS A Major Climate Driver Emerges for the First Time in Three Years.
Durling Recent Weeks, Changes in Ocean Tempics Show The Development of a Negative Indian Ocean Dipole (IOD) – The Wet Phase of the Indian Ocean, Whiche Rivals La Niña for Its Positive Impact on Australia’s Rainfall.
Negative iOods in the Past Have Contrabied to Most of Australia’s Wettest Winters and Springs on Record, Including All Four Previoous Episodes This Center in 2010, 2016, 2021 and 2022.
The Key Monitoring Regions for An IOD Show Cooling of the Coast of Africa and Warming Near Indonesia. (Source: Noaa))
The ‘La Niña of the West’
A Negative IOD Refers to A. Prong Period of At Least Eight Weeks of Warmer Waters Near Indonesia and Cooler Waters of the Horn of Africa.
Who is this May Seem IncONSEQUNTIAAL, The Change Corresponds with a Shift in the Overlying Pressure and Wind Regime – Specificylly, There is Increase in Moist Air Blowing Towars Australia’s Longituds 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 the Critical for the Continued Evolution of Ant and Its Eventonal Impact on the Weather is that the Changes to the Ocean and Atmosphere Reinforce Each Other Thrug A Positive Feedback Loop – a coupling that can prepare the Anomalous State for Months.
Convection, Cloud and Rain Increase Over Australia’s Longituds Durling A NEGATIVE PHASE of the IOD. (Source: bom))
First Negative IOD In Three Years
Negative IODS, and their Counterpart Positive IODS, on average occur every one in Five Years.
How, the Indian Ocean Has Been ExceptLly Active During the Past Decade, with Only Three Years (2017, 2002 and 2024) Remaining Neutral.
The Prospect of a NEGATIVE IOD RTURINING in 2025 was First Flagged by the Bureau of Meteorology (BOM) Back in AUTUNN when are their light-shipping was showing the Driver WV Likely Develop at some Point in Winter.
Despite Little Observational Verification, The Bom’s Modelling Consently Stuck to that Predgestion Through June.
Howver, Water Tempics of the East Coast of African Began to Drop Notable in July.
The index used to measure the stea of the indian Ocean reflecated this change, and iTS LATEST Weekly Value Sits at -0.6 Degrees Celsius, below the Negative IOD ThrestHold of -0.4 ° C for The Second Conatecutive Week.
The Bom’s Modelling Shows NEGATIVE IOD CONDITIONS Will Intensify Further InTo Early Spring and Remain Until December. (Source: bom))
Howver, 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 applyers increesingly Likely with the Latest Modeling Showing the Index Falling to Around -1 ° C in September Before Gradually Climbing Back to Neutral in December, Easily, Easily, Easily, Easily, Easily SUFFICIENT TIME to Have a Lasting Impression on the National’s Weather.
Major Boost to Winter and Spring Rainfall
The Life Span of An IOD Event is Shorter Than Pacific El NIñO-La Niña Episodes, Whiche Normally Last About Nine Months.
A TyPical IOD Will Develop in Winter, Quickly Peak, then Decay by Early Summer when the Monsoon Eralodes Any Influence on Tropical Indian Ocean Winds.
The Impacts, Shown in the Table Below, Are Most PRONONED in Spring when IOD Events from 1960 to 2024.
Winter SEES An Averge 20 Per Center to Precipitation, and by Summer it Falls to 13.9 Per Center.
In TERMS of Spatial Extrent, 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 Decle-Rainfall Totals in the Top 20 Per Cent of All Years.
An Averge of Nine Classic Past Negative IOD Years Have Shown a Clear Increase in Rainfall Across Most of Australia. (Source: bom))
Howver, 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 use during
The Most Accurate Forecast for Seasoning 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.
The Latest Spring Outlook Favors Above-Median Rainfall Across Most of Australia with the Greatist Likelihood Over the Eastern Inland. (ABC News))
Another Impact of a Negative IOD is on Tempteratures.
Climate Change Encies Most Australian Seasons Are Comfortably Warmer Than Normal, Howver, During Extended Wet Periods, The Additional Cloud Cover Can Lower Dayime Tempervies.
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.
