It's been a slow start to northern Australia's wet season, but a burst of tropical rainfall - and potentially increased tropical cyclone activity - could be on the horizon.

Australia's wet season runs from October to April, although rainfall doesn't really ramp up in our tropics until the monsoon arrives over northern Australia.

What is the Monsoon?

The monsoon refers to a pattern of moisture-laden northwesterly winds that can bring prolonged, and often heavy periods of rainfall to northern Australia. Each wet season, we usually experience around two or three active phases of the monsoon, separated by inactive phases, which are also called monsoon 'breaks.'

Most of northern Australia's wet season rainfall occurs during active phases of the monsoon. During inactive phases, the northwesterly winds ease over northern Australia, leading to a period of more settled and often drier weather in the tropics.

The first arrival of the monsoon in Australia each season, which is referred to as the monsoon onset, usually occurs around late-December. However, it's running a few weeks late this season and still hasn't arrived.

Image: Active monsoon phases usually cause periods of frequent and heavy rain in northern Australia.

The Madden Julian Oscillation (MJO)

In addition to the regular monsoon cycle, rainfall during Australia's wet season is influenced by the Madden Julian Oscillation (MJO).

The MJO is a pulse of increased cloud and rain - also known as convective activity - that travels around the globe near the equator every 30-60 days. Like the monsoon, the MJO alternated between active and inactive phases as it circumnavigates our globe.

When the MJO passes near Australia in an active phase, it can enhance monsoonal rainfall and increase the chance of tropical cyclone development. These effects are most prominent when the MJO is in a strong active phase while it passes near northern Australia.

Burst of tropical activity possibly on the horizon

A number of forecast models indicate that an active phase of the MJO could pass near Australia's tropics later this week or next week. This could cause a burst of increased convective activity near northern Australia and may help the monsoon develop near northern Australia. An active MJO would also provide more favourable conditions for tropical cyclones to develop near Australia.

While the monsoon onset and tropical cyclone activity are not guaranteed during the next couple of weeks, there are a few things lining up that may increase their likelihood. If you live or plan on travelling to northern Australia, be sure to stay up to date with the latest forecasts and warnings during the next fortnight.