An active tropical cyclone season was promised, but has this been delivered?

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Coming into the 2020/21 tropical cyclone seasons, all signs were pointing towards an above-average number of cyclones in the Australian region.

So far this season, this hasn’t eventuated. So what happened?

The tropics have actually been very active this season with 17 tropical lows generating widespread rainfall and strong winds across northern Australia. At times, the rainfall moved to the south of the country, with the whole country recording its third wettest December on record.

Despite the high number of tropical lows that have formed, only six have developed into tropical cyclones. This falls well below the average of nine to eleven a season.

This went against expectations because we were primed for an above normal tropical cyclone season owing to La Niña and warm oceans across northern Australia (figure 1). The warm oceans are one of the ingredients cyclones need to develop  – think of the oceans as their energy source or fuel.

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Figure 1: NOAA Sea Surface Temperature (SST) anomalies on the 1st of March 2021.

So why have there been so few cyclones this season?

Firstly, many of the low pressure systems have developed on or near the coastline, which has deprived them of their ‘fuel’ (warm ocean) that they need to develop.

Secondly, the wind setup has not been quite right, with opposing winds at different heights in the atmosphere, breaking the storm apart and working against each other.

Finally, the season is not over, we have a few months to go and March is usually the most active month. Never fear our meteorologists will be watching any tropical low development in the next few months. https://business.weatherzone.com.au