Weekly Tropical Climate Note

Australian tropical cyclone season 2018-19 commences

The tropical cyclone season for Australia officially spans the period 1 November to 30 April. While out-of-season tropical cyclones can occur, the vast majority of tropical cyclones in the Australian region occur during these months. Tropical cyclones in November are relatively rare, but since 2000, eight tropical cyclones, or tropical lows which subsequently strengthened to tropical cyclone intensity, developed in the Australian region in November. This includes two severe tropical cyclones (category 3 or stronger).

On average, 11 tropical cyclones form in the Australian region each season, four of which typically cross the coast. The Australian Tropical Cyclone Outlook for 2018-19 released in early October indicates fewer than normal tropical cyclones are expected in the current season. The El Niño–Southern Oscillation is the primary climate driver influencing this outlook. El Niño typically reduces the number of tropical cyclones and coastal crossings in Australia. However, at least one tropical cyclone has crossed the Australian coast each season since reliable records began in the 1970s, regardless of the state of climate drivers.

Learn more about tropical cyclones.

El Niño ALERT continues—dry start to wet season likely

The Bureau's ENSO Outlook remains at El Niño ALERT, meaning there is approximately a 70% chance of El Niño occurring in the coming months. Temperatures of the tropical Pacific Ocean have exceeded El Niño thresholds for the past fortnight, with models predicting further warming of the ocean is likely. However, ENSO atmospheric indicators (such as the Southern Oscillation Index and cloudiness near the Date Line) are yet to indicate that the ocean and atmosphere have coupled and are reinforcing each other. Coupling is needed to sustain an El Niño event.  

The Indian Ocean Dipole (IOD) index dropped slightly in the last week, but has been mostly above the threshold of +0.4 °C during the last 2 months. As a result, 2018 will be classified as a positive IOD year. The majority of models surveyed by the Bureau suggest IOD index values are likely to return to neutral during November.

El Niño and a positive IOD at this time of the year increase the likelihood of a drier than usual start to the northern wet season for Queensland and the Northern Territory.

See the Bureau's current ENSO Wrap-Up for more information.

Madden–Julian Oscillation strengthens over Indian Ocean

A pulse of the Madden–Julian Oscillation (MJO) moved eastwards across African longitudes and into the tropical Indian Ocean during the past week. At this time of the year, the MJO in this region typically suppresses cloudiness and rainfall over South-East Asia and the Maritime Continent and enhances convection over the tropical Indian Ocean. With the retreat of the southwest Indian monsoon, rainfall over India at this time of the year is predominantly due to seasonal northeasterly winds, a wind flow which would typically be reinforced by the easterly winds associated with the current MJO pulse.

The MJO pulse also coincided with the formation of tropical cyclone Alcide in the southwest Indian Ocean, near Madagascar.

Climate models are in good agreement that this MJO pulse will track further east over central and eastern parts of the Indian Ocean and weaken during the next seven days. However, the extent to which the MJO pulse weakens is unclear from the forecasts.

See the Bureau's current MJO monitoring for more information on the MJO.