Tropical Climate Update

Madden-Julian Oscillation predicted to strengthen

The Madden–Julian Oscillation (MJO) signal has been weak or indiscernible for the last few weeks, and has not been a significant driver of tropical rainfall patterns. In the coming week, most international climate models surveyed by the Bureau of Meteorology predict the MJO will strengthen and move over the Maritime Continent and the western Pacific Ocean. At this time of the year, such a scenario would typically lead to enhanced cloudiness and rainfall over northern parts of the Maritime Continent and over the northwest Pacific region. Far northern parts of Australia, especially Cape York, may also experience a marginal increase in cloudiness and rainfall.

Although it is early in the season, while the MJO is active over the next two to three weeks, the risk of tropical cyclone development is elevated, especially over the Coral Sea.

See the Bureau's MJO Monitoring for current MJO information.

More cyclones than average for 2016-17 in Australian region

Today is the official start date of the Australian 2016-17 tropical cyclone season, which will run through April 2017. The recently released tropical cyclone outlook  predicts an average to above-average number of cyclones for the Australian tropical cyclone season. This outlook is mostly influenced by the neutral to weak La Niña conditions in the tropical Pacific Ocean and warmer than average ocean temperatures off Australia’s northern coasts. La Niña years are typically associated with above-average tropical cyclone numbers, and an earlier than normal date for the first cyclone to impact Australia. Since satellite observations have been available, the long-term average number of tropical cyclones in the Australian region is 11. Last season (2015–16) saw the lowest number of tropical cyclones, with only three. The most active seasons were 1973-74 (a La Niña year) and 1983-84 (following an El Niño year), each with 19 tropical cyclones.

Negative Indian Ocean Dipole and ENSO-neutral conditions continue

A negative Indian Ocean Dipole (IOD) continues, but is weakening. Models predict the IOD will return to neutral by the end of November. During a negative IOD event, rainfall across northern Australia is typically above average from September to November, with warmer daytime and night-time temperatures often experienced.

In the tropical Pacific Ocean, the El Niño–Southern Oscillation (ENSO) remains neutral. Six of eight climate models indicate the tropical Pacific is likely to remain at ENSO-neutral levels in the coming months. However, two models indicate weak La Niña levels will be reached, hence the ENSO Outlook remains at La Niña WATCH.

Even if La Niña thresholds are not met, warmer waters to the north of Australia mean La Niña-like impacts are possible in the coming months. During La Niña, northern Australia typically experiences above-average wet season rainfall, including increased rainfall during the ‘build-up’ months.

See the Bureau’s ENSO Wrap-Up for official El Niño, La Niña and IOD information.