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Rain systems still starved of moisture

Ben Domensino, Wednesday September 26, 2018 - 12:39 AEST

Cooling waters to the northwest of Australia may extend the run of abnormally dry weather that's affecting large swathes of the country into late spring.

It's been a dry year to date for many parts of the country. Southern Australia experienced its second driest autumn on record, which was followed by the 14th driest winter in 119 years of records for the country as a whole. Now, most of Australia has registered less than 20 per cent of their average September rainfall during the first 26 days of the month.

While cooler than average water near Australia has contributed to the dry weather in recent months, this year's lack of rain to date has, impressively, occured in the absence of both El Nino and a positive Indian Ocean Dipole - two climate drivers that promote dry weather in Australia. However, these dry-weather inducing events remain possible in the months ahead.

A positive IOD occurs when cooler-than-usual water sits to the northwest of Australia and abnormally warm water lies on the other side of the Indian Ocean, near Africa. This pattern weakens the flow of westerly winds across the equatorial Indian Ocean and reduces the amount of atmospheric moisture to the northwest of Australia. Below average rainfall is often observed across much of Australia during a positive IOD.

According to the Bureau of Meteorology, the IOD index exceeded the positive threshold during the last fortnight. This trend needs to be sustained for a few more weeks for it to be classified as a positive IOD event. At present, four out of the six climate models surveyed by the Bureau indicate that this will be the case as we move into October.

While the Indian Ocean is leaning towards drier weather in the coming weeks, the Pacific Ocean may be showing signs of moving away from the El Nino that has been threatening to develop in the past few months. Recent cooling in the tropical Pacific Ocean indicates that neutral conditions may persist for the rest of 2018, although Australia remains on El Nino Watch for the time being.

El Nino occurs when cooler-than-usual water is located to the northeast of Australia near the equator and abnormally warm water lies off the west coast of South America, near Peru.

Visit http://www.bom.gov.au/climate/ for the latest climate updates.

- Weatherzone

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