Currently, there are six tropical lows identified in the Bureau's Tropical Cyclone 7 day forecast. Two out of six of these tropical lows have a moderate chance of developing into a tropical cyclone across Australian waters within the next 7 days. The next three tropical cyclones to be named within the Australian area of responsibility will be Taliah, Vince and then Zelia, respectively, following the Bureau's alphabetical list of approved names. So, what causes a tropical low to become a cyclone?