Weekly Tropical Climate Note

Official end of the northern Australian wet season approaches

While the official end of the 2018–19 northern wet-season is 30 April, dry season-like weather patterns have already developed over northern Australia. The monsoon has retreated, and southeasterly Trade Winds have developed over northern Australia. While the humidity has fallen, there has still been enough moisture in the air to result in some shower activity, especially along the east coast of Queensland.

The Bureau's Climate Outlooks indicate this dry season is likely to be warmer than average, which implies a continuation of the warmer than usual conditions experienced over the summer period. 

Tune in next week for a summary of the 2018–19 wet season.

Madden–Julian Oscillation heading to Australian longitudes

After a lengthy period with no activity, in recent days a Madden–Julian Oscillation (MJO) signal has been detected in the tropical Indian Ocean. Cloudiness over the equator near India has increased this past week, while cloudiness has been suppressed over the Maritime Continent—a typical MJO cloud pattern for a signal detected in the Indian Ocean.

Most climate models indicate the MJO signal will progress eastwards, reaching the Maritime Continent in the last days of April. However, models vary in how strong they predict the MJO will be, with some predicting a very weak signal.

At this time of the year, the MJO has a weak effect on Australian weather, as it is typically too late in the season to trigger a monsoon burst, although it can lead to an increase in humidity and shower activity in the northern tropics.

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

Short-lived El Niño remains likely

Ocean temperatures in the tropical Pacific are close to El Niño thresholds, but the atmosphere has yet to respond. For example, the Southern Oscillation Index, which typically drops when an El Niño pressure pattern develops across the equatorial Pacific, remains neutral and trade winds are currently close to normal strength near the equator.

Despite this lack of atmospheric response, a majority of climate models indicate an El Niño is still likely in the coming months, though most indicate it will be a short-lived event. The Bureau's ENSO Outlook remains at El Niño ALERT which means the chance of El Niño developing in the coming months is approximately 70%.

El Niño typically brings drier than average conditions for eastern Australia during winter–spring, and warmer days across southern Australia—it has little impact on the Australian tropics at this time of year.

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