Weekly Tropical Climate Note
Tropical low to generate widespread rain across northeast Australia this week
A tropical low currently near the southern coast of the Gulf of Carpentaria is expected to be the focus of locally heavy rain for the next few days. This comes after a week of significant rainfall across much of northern Australia, associated with a burst of moist westerly winds across the region. As a result, some locations, particularly across inland northern Queensland, are expected to experience flooding (see latest flood warnings at National Warnings Summary page).
The tropical low is expected to remain over land and track westwards through the Northern Territory in the next day or two. Later this week, the low is expected to be captured by a mid-latitude trough, and likely bring tropical moisture and heavy rainfall to southeastern Australia.
Widespread rainfall across the north, but monsoon onset yet to arrive at Darwin
Despite the widespread heavy rain across parts of tropical Australia during the past week, the technical definition for monsoon onset was not met at Darwin. This means that this wet season, 2019–20, will observe the latest monsoon onset since records commenced in 1957–58. The previous latest onset at Darwin Airport (where, by convention, it is measured) was 25 January 1973.
The recent monsoon-like conditions at Darwin did not meet the technical definition of monsoon onset that is used to compare against past years. Moist westerly wind flow across the Top End, which contributed to the widespread rainfall, started its life in the mid-latitudes of the Southern Hemisphere (i.e. from the south), whereas true monsoon westerlies cross the equator from the northern hemisphere. A sustained, deep monsoonal circulation was also absent, meaning the winds in the upper atmosphere were also not typical of a monsoon. While this technical definition of the Australian monsoon onset was not met, if the monsoon definition was applied to locations other than Darwin, there may very well have been regions of 'monsoon onset'. The current climate conditions across northern Australia mean that monsoon onset at Darwin is at least a week away.
Madden–Julian Oscillation becomes weak
The Madden–Julian Oscillation (MJO) rapidly weakened as it tracked across the tropical central Pacific Ocean and is now indiscernible. It is not expected to strengthen significantly in the coming week, although some climate models predict it may strengthen and briefly move into the eastern Maritime Continent or western Pacific Ocean. Given forecasts indicate only limited and brief development of an MJO pulse, a significant influence on rainfall across northern Australia due to the MJO is not expected in the coming fortnight.
Read more about the Madden–Julian Oscillation
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