Frequently Asked Questions (FAQ)

Climatology | Impacts | Extremes| TCs affecting WA towns | Forecast Accuracy
Frequently Asked Questions | Annual summaries

Definitions | Characteristics and Formation | Climatology | Extremes | Forecasting | More Information

Climatology

5. What determines the movement of tropical cyclones?

One look at the tracks of cyclones in the Australian region (see map) shows that cyclones can move in many different directions. However, cyclones off the northwest coast do have a preferred movement. Typically they are initially steered to the westsouthwest at speeds of 5-20 km/h and then take a more southerly track as they move further to the south. If they do move south of about 22°S or cross the Pilbara coast they tend to curve to the south-southeast and accelerate. Those that affect the lower part of the west coast may reach speeds of over 60 km/h.

However, the path of each storm varies considerably in response to the weather patterns occurring at the time. Tropical cyclones can be thought of as being steered by the surrounding environmental flow particularly in the middle parts of the atmosphere (from about 2 to 6 km above the surface). The larger and more intense systems do influence the surrounding environment and in so doing affect their movement. Short-term fluctuations in the track are common for intense cyclones, for example Bobby (1995) made several loops and changed speed as it approached the Pilbara coast (see track of Bobby based on radar observations).