It's running very late this year, but the monsoon trough is approaching northern Australia and will increase tropical activity over the coming days.

A late onset of the west season and a delay of an established monsoon trough has led to rainfall deficiencies in some areas of northern Queensland, the Top End and the Kimberley, some severe over the last eight months. Rain is on the way, however, with the monsoon trough likely to be over the northern tropics by late this coming weekend.

Alongside the seasonal rains and increased cloud cover, the monsoon trough also increases the chances of low pressure systems forming within it. Most of the lows remain that way, not deepening enough to develop into cyclones. But when the Madden-Julian Oscillation (MJO) is nearby, the chance of cyclones forming increases, and the MJO is nearby.

The MJO is an atmospheric disturbance, moving wavelike from west to east near the equator, and it passes northern Australia every 30-60 days in summer. In winter, the MJO is over the other side of the equator. Currently, the MJO is in our neighbourhood, and models are leaning towards an increased chance of tropical cyclone formation.

If a tropical cyclone was to form over the coming days, it will most likely be over the Coral Sea. Conditions are a little more favourable there than off the northwest WA coast, but the Gulf of Carpenteria is also plenty warm enough to fuel a cyclone.

As tropical lows and cyclones are such dynamic systems, models can sometimes struggle with forecasting genesis, and track, should one form. As of Thursday afternoon, the chances of a tropical cyclone forming were low, however, that chance may increase on Friday as models are starting to agree with each other. The next tropical cyclone to form in Australian waters will be called Penny.