Millions of residents along Australia’s eastern coast are bracing for the arrival of a very slow-moving storm, the strongest tropical cyclone to threaten the region in more than 50 years. Tropical Cyclone Alfred is expected to make landfall late Friday or early Saturday with the strength of a category 1 Atlantic hurricane,

Australia braced for a rare east coast tropical cyclone that is swirling towards Brisbane, its third-most populous city, with authorities urging residents in flood-prone suburbs to evacuate soon.

Cyclone Alfred is unusual for two reasons — it has formed way too south, and is moving slowly. Both these factors make it more dangerous. We explain why.