THE strong positive Indian Ocean Dipole (IOD) event continues to bring below-average rainfall to southern Australia, while the El Niño–Southern Oscillation (ENSO) remains neutral, according to the latest report from the Bureau of Meteorology.
The IOD index remains strongly positive, with the latest weekly value at +2.06 °C, well above the positive IOD threshold of +0.4 °C.
Strong easterly trade winds across the tropical Indian Ocean have maintained cooler than average waters in the eastern Indian Ocean and warmer than average waters off the Horn of Africa.
Forecasts show an easing in the easterly trade winds in the coming weeks, suggesting the positive IOD may be near its peak.
However, international climate models surveyed by the Bureau indicate the positive IOD is so strong that it is likely to take several weeks to decline and could persist into mid-summer.
The slow decline is also due to the strong IOD slowing the movement of the monsoon into the southern hemisphere.
Typically, it is the movement of the monsoon over Indonesia during December that ends IOD events.
A positive IOD typically brings below average spring rainfall to southern and central Australia, with warmer days for the southern two-thirds of the country.
Positive IOD events are often associated with a more severe fire season for southeast Australia.
In the tropical Pacific Ocean, waters have warmed over the past month but have caused little change in the atmosphere, and hence the El Niño–Southern Oscillation (ENSO) remains neutral.
The latest 30-day Southern Oscillation Index (SOI) is –5.2, returning it to more neutral levels.
The majority of climate models forecast neutral ENSO for the remainder of 2019 and into the first quarter of 2020.
When ENSO is neutral, it has little effect on Australian and global climate, meaning other influences are more likely to dominate.