Tropical Climate Update

Thunderstorms and heavy rainfall continue across northern Australia

Scattered showers and thunderstorms have continued across northern Australia during the past week. A trough directed tropical moisture and brought rain and thunderstorms to the central and southern Northern Territory, Queensland, and south-eastern Australia early in December.

Weekly rainfall totals, to 9 December of 50 to 100 mm were recorded across parts of northern Australia between 3 and 9 December with over 100 mm recorded in the Top End of the Northern Territory and isolated parts of the Kimberley in Western Australia. Weekly totals greater than 200 mm were recorded in parts of Cape York Peninsula, the North Tropical Coast and Tablelands districts in Queensland. The heaviest daily rainfall (at a Bureau gauge) in the Northern Territory was 105.0 mm at West Waterhouse on the 3rd, whilst Curtin Aero in the west Kimberley in Western Australia recorded a daily rainfall of 112.8 mm on the 8th. For Queensland, the highest daily total (at a Bureau gauge) was 158.0 mm at Highbury Station in Queensland in the 24 hours to 9am on the 4th.

Ocean temperatures off the north-west coast of Australia are currently 2 to 3 °C warmer than average. Significantly warmer than average ocean temperatures increase the available moisture for rainfall.

The long-range forecast for the fortnight of 14 to 27 December shows rainfall is likely to exceed average across northern Western Australia, the Top End coast of the Northern Territory, and Cape York Peninsula in Queensland. There is an increased chance of an unusually wet fortnight (the highest 20% of fortnightly rainfall observations in December from 1981 to 2018) in Western Australia's north, most likely associated with tropical lows or possible tropical cyclone development. Maximum temperatures for the fortnight are likely to be cooler than average in the same areas are forecast to be impacted by wet conditions. There is an increased chance of an unusually cool fortnight (the lowest 20% of fortnightly maximum temperature observations in December from 1981 to 2018) in the north of Western Australia, the Top End of the Northern Territory, and across the Cape York Peninsula in Queensland.

Multiple tropical lows in the Australian Area of Responsibility

Tropical low 02U slowly developed to the north of Western Australia's Pilbara coast on 9 December. As at 10am AEDT 10 December, tropical low 02U was expected to move towards the west south-west and remain well offshore before weakening later this week in an unfavourable environment.

In the far west of the Australian Area of Responsibility, tropical low 04U formed on 7 December, to the north of the Cocos (Keeling) Islands. As at 10am AEDT 10 December, tropical low 04U is forecast to remain slow moving eastward before dissipating later this week. Increased shower and thunderstorm activity is forecast for the Cocos (Keeling) Islands during the next few days.

Another tropical low 05U is expected to develop in the Timor Sea north of the Kimberley region and track south-west near the coast of Western Australia later in the week. As at 10am AEDT 10 December, forecasts indicate 05U may develop to tropical cyclone intensity later in the week or during the weekend as it approaches Western Australia's Pilbara coast.

For further information, refer to the Tropical cyclone 7 day forecast  for regular updates to forecast tropical activity.  

Madden–Julian Oscillation moves into the eastern Maritime Continent

A moderately strong Madden–Julian Oscillation (MJO) pulse moved slowly eastward over the Indian Ocean and Maritime Continent during the past fortnight.  The MJO is currently (as at 7 December) located over the eastern Maritime Continent.

The majority of climate models indicate the MJO will maintain its slow eastward movement into the Western Pacific in the coming fortnight.  Some models indicate the MJO will weaken during the third week of December.   

An active MJO tracking across the Maritime Continent, northern Australia and the Western Pacific, brings an increased risk of tropical cyclone and tropical low development in the Australian region.  The formation of tropical lows 02U and 04U in the Western Region of the Australian area of Responsibility during the past week, and the expected development of another tropical low 05U over the Timor Sea or Arafura Sea in the coming days has coincided with this passing MJO pulse.

A strong westerly wind burst brought monsoonal conditions over the west and south of Indonesia during the past week and is expected to extend further east over northern Australian waters in the second week of December.