Weekly Tropical Climate Note

A dry end to the year for northern Australia

The latest rainfall outlook issued by the Bureau indicates a high likelihood of drier-than-average conditions across much of northern Australia until the end of the month. Only parts of northwestern Western Australia are forecast to have a greater than 50% chance of above-average rainfall during that time. The rainfall signal becomes more neutral from January, when much of northern Australia has a roughly 50-50 chance of receiving average rainfall.

The dominant climate influence over northern Australia remains the positive Indian Ocean Dipole (IOD). The current event peaked during October and has gradually weakened since the start of November. The latest weekly value of +0.9 °C is still well above the threshold of +0.4 °C, hence the ongoing significant influence it continues to have across much of Australia. Nearly all climate models indicate the positive IOD will continue to weaken, and dissipate in January 2020.

Low-level wind analysis shows there is still no tropical trough south of the equator—a feature that is usually well established by this time of the year and is a precursor to the formation of a monsoon trough in the southern hemisphere. This suggests there is a high probability of a delayed monsoon onset for Australia in 2019–20.

Read more about the Indian Ocean Dipole

Weak Madden–Julian Oscillation to have minimal influence on Australian rainfall

A weak pulse of the Madden–Julian Oscillation (MJO) is expected to develop over the western Indian Ocean in the coming days. This pulse is forecast to be short-lived, however, and is expected to rapidly weaken later in the week as it encounters the influence of the positive IOD over the eastern Indian Ocean. As such, the MJO is unlikely to exert a significant influence on rainfall patterns across northern Australia and the Maritime Continent during the next fortnight.

Read more about the Madden–Julian Oscillation

Tropical cyclone activity in both hemispheres

In the southern hemisphere, tropical cyclone Belna made landfall on northwestern Madagascar in recent hours. At the time of landfall, Belna had estimated sustained winds in excess of 157 km/h, equivalent to an Australian category 3 tropical cyclone. Belna is expected to weaken rapidly in the coming hours as it tracks further south across the island.

In the northern hemisphere, typhoon Kammuri (Tisoy) made landfall over the northern Philippines on 3 December, generating strong winds and heavy rain. Kammuri (Tisoy) entered the record books by having the coldest cloud-top temperatures ever recorded, -109.4 °C. This exceeded the previous coldest of approximately -103 °C, associated with tropical cylone Hilda which formed off the Queensland coast in 1990. Such an extreme temperature indicates that the clouds extended very high into the lower atmosphere (known as the troposphere), as a result of intense updrafts near the centre of the typhoon.

Product code: IDCKGEW000

Further information

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