Madden-Julian Oscillation (MJO)

Slight weakening of positive Indian Ocean Dipole

The positive Indian Ocean Dipole (IOD) weakened marginally during the past week. This is likely due to interference with the Madden–Julian Oscillation as it moved over the eastern Indian Ocean and therefore unlikely to be an indication of the imminent decay of the positive IOD. The most recent weekly value of the IOD index was +1.7 °C, down from +2.0 °C the previous week. The threshold for a positive IOD is a sustained value of +0.4 °C or greater, so the current event remains strong.

The influence of the positive IOD is reflected in the latest rainfall outlook issued by the Bureau, which indicates a high likelihood of below-average rainfall for much of northern Australia for the remainder of November and throughout December. The positive IOD is also likely to lead to a delay in the onset of the Australian monsoon in 2019-20. Climate models surveyed by the Bureau indicate the positive IOD is so strong that its breakdown is likely to take longer than usual. The decay of the IOD is associated with the seasonal development of a monsoon trough in the southern hemisphere around December, but this process is well behind its typical schedule and is likely to happen significantly later than usual in 2019. As a result, the influence of the IOD is expected to persist into January 2020.

Read more about the Indian Ocean Dipole.

Madden–Julian Oscillation maintains strength over Pacific Ocean

A moderate to strong pulse of the Madden–Julian Oscillation (MJO) is rapidly tracking eastwards across the tropical Pacific Ocean. Climate models predict the MJO will track from the central to eastern Pacific Ocean in the coming week and then approach the Americas in the following week. At this time of the year, an MJO pulse over the central Pacific Ocean would typically enhance rainfall over parts of northern Australia and the southern Maritime Continent. However, due to the rapid movement of the MJO pulse and the adverse local environment associated with the positive IOD, the presence of the MJO is unlikely to lead to widespread above-average rainfall. As the MJO moves over the eastern Pacific Ocean, and further east, cloudiness and rainfall across northern Australia, the Maritime Continent and much of South-East Asia is typically suppressed. The combination of the positive IOD and the suppressed component of the MJO increases the likelihood of below-average rainfall occurring across the Australian tropics in the coming fortnight.

Read more about the Madden–Julian Oscillation.

Two tropical cyclones impact Asia in recent days

Tropical storm Nakri made landfall on the southeast Vietnam coast during Monday morning, generating locally heavy rain and strong winds. Nakri weakened to below-typhoon strength (Australian category 3 equivalent) prior to reaching the coast of Vietnam. Nakri has weakened to below tropical cyclone intensity.

Cyclonic storm Bulbul, which formed from the remnants of ex-tropical storm Matmo, made landfall over West Bengal, in northeast India, on Monday night and then moved over Bangladesh. A dangerous storm surge, heavy rainfall and damaging wind gusts occurred as Bulbul moved ashore. This storm has now dissipated and adverse weather conditions in the area have eased. Bulbul peaked at hurricane strength (equivalent to a typhoon, or Australian category 3 or greater system), making it the sixth storm of such intensity to develop over the northern Indian Ocean in 2019. This is the highest number of hurricane-strength storms ever recorded in this region in a single season.

Two other developing tropical lows over the western North Pacific Ocean have the potential to develop into tropical cyclones in the next day or two. While one system is over open waters well to the southeast of Japan, the other low is just to the east of the Philippines and forecast to move towards the island group in the short term.

 Tropical cyclone information for this region available at the Japan Meteorological Agency.