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Posted by: tropicalbomb Offline Posted: Monday, 14 October 2019 8:20:56 PM(UTC)
The BOM are issuing weekly tropical outlook statements

Weekly Tropical Climate Note

8 October 2019 Next issue 15 October 2019
Dry start to northern wet season likely for 2019-20

By convention, the northern Australia wet season commences 1 October and runs until 30 April.

Based on recent climate outlooks issued by the Bureau, rainfall across much of northern Australia is highly likely to be below average between now and the end of the year.

The primary climate driver currently influencing the rainfall outlooks over Australia, and the Maritime Continent further north, is the Indian Ocean Dipole (IOD). Currently, the IOD is strongly positive (in fact, the most recent weekly value of +1.94 is the highest on record since at least 2001), and it is likely to remain positive until at least December.

With a positive IOD, rainfall between October and December is typically below average across the Northern Territory and much of northern Queensland. Northern Western Australia (WA) is not significantly influenced by a positive IOD at this time of the year, and so the rainfall outlooks suggest there is about a 50% chance of observing above-average rainfall over the next three months.

Climate models also predict that waters off the northern WA coast will warm in the coming months, and this would likely increase the probability of enhanced rainfall across coastal northern WA.

While rainfall over northern Australia and the Maritime Continent is typically reduced during a positive IOD, it usually contributes to enhanced rainfall across the northwest Indian Ocean and over the Indian subcontinent. It is likely that the above-average cumulative rainfall India observed during the 2019 monsoon season (June to September) is associated with the positive IOD. By October, the Indian monsoon is typically in retreat mode and tracking southwards and weakening. However, the monsoon remains active across India and has yet to commence its annual withdrawal, which typically starts in northern India from early September (further information from the UK Met Office here).
Madden–Julian Oscillation to rapidly weaken

A pulse of the Madden–Julian Oscillation (MJO) over the western Indian Ocean is expected to weaken rapidly in the coming days and become indiscernible.

The rapid weakening of the MJO is likely related to the strong positive Indian Ocean Dipole. The strengthened easterly winds which become established over the Indian Ocean with a positive IOD typically weaken the MJO as it progresses into the eastern tropical Indian Ocean. As a result, it is unlikely that a strong pulse of the MJO will influence the eastern Indian Ocean, including northern Australia and the Maritime Continent, until the IOD has weakened significantly. This also implies that there is a low likelihood of enhanced rainfall due to MJO activity over the Australian tropics, and further north, until late in 2019.

Read more about the Bureau's MJO monitoring.
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