Passage: "Typhoon preparedness begins long before a storm arrives. Families are advised to prepare a go-bag containing water, food that does not need cooking, a flashlight, a whistle, medicines and copies of important documents. They should also know the evacuation centre nearest their home and the safest route to reach it. When authorities order a pre-emptive evacuation, residents of high-risk areas should leave early, while roads are still passable, rather than wait until floodwaters rise." According to the passage, when does typhoon preparedness begin?