and heaviest rainfall. Tropical cyclones derive their energy from the warm tropical oceans and do not form unless the sea-surface temperature is above 26.5C, although once formed, they can persist over lower sea-surface temperatures. Tropical cyclones can persist for many days and may follow quite erratic paths. They usually dissipate over land or colder oceans. Most of the northern coastline of Australia is covered by the Bureau's weather radar network. For real time images and radar information, see: www.bom.gov.au/weather/radar/ Cyclone danger and impacts Tropical Cyclones are dangerous because they produce destructive winds, heavy rainfall with flooding and damaging storm surges that can cause inundation of low-lying coastal areas. Cyclones have wind gusts in excess of 90 km/h around their centres and, in the most severe cyclones, gusts can exceed 280 km/h. These very destructive winds can cause extensive property damage and turn airborne debris into potentially lethal missiles. It is important to remember that, during the passage of the cyclone centre or eye , there will be a temporary lull in the wind, but that this will soon be replaced by destructive winds from another direction. Heavy rainfall associated with the passage of a tropical cyclone can produce extensive flooding. This can cause further damage and death by drowning. The heavy rain can persist as the cyclone moves inland and decays, hence flooding due to a decayed cyclone can occur a long way from the tropical coast as the remains of a cyclone move into central and southern parts of