Alert! BOM predicted Positive IOD likely to occur
BOM, 12 Sep 2023
Positive IOD very likely to emerge; El Niño Alert continues
The long-range forecast for Australia indicates warmer and drier than average conditions are likely across most of southern and eastern Australia from October to December. The Bureau’s climate model takes into account all influences from the oceans and atmosphere when generating its long-range forecasts.
The Bureau’s El Niño Alert continues, with El Niño development likely during spring. When El Niño Alert criteria have been met in the past, an El Niño event has developed around 70% of the time.
Sea surface temperatures (SSTs) in the tropical Pacific are exceeding El Niño thresholds and have continued to warm slightly over the last fortnight. Climate models indicate further warming of the central to eastern Pacific is likely, with SSTs remaining above El Niño thresholds until at least early 2024.
The 90-day Southern Oscillation Index (SOI) is currently -7.4, exceeding El Niño thresholds. Trade winds for August 2023 were slightly weaker than average across the Pacific for the first time since January 2020. Other atmospheric indicators have also recently shown signs of possible coupling between the Pacific Ocean and the atmosphere. This coupling is a characteristic of an El Niño event and is what strengthens and sustains an event for an extended period. El Niño typically leads to reduced spring rainfall for eastern Australia.
The Indian Ocean Dipole (IOD) index is +1.13 °C for week ending 10 September. This is its fourth week above the positive IOD threshold (+0.40 °C), with the recent high values (above +1.0 °C) indicating an event is very likely. If the IOD index continues to remain above this threshold, a positive IOD event will be considered underway. All models indicate this is highly likely and that a positive IOD will be sustained to at least the end of spring. A positive IOD typically decreases spring rainfall for central and south-east Australia and can increase the drying influence of El Niño.
A weakening Madden–Julian Oscillation (MJO) pulse recently moved into the western Maritime Continent. Most models forecast this pulse to become indiscernible in the coming days.
Source: BOM, ENSO Outlook
