Depending on the circumstances of a natural disaster that is? If it's not serious, it can be told in time around. But if serious people should let you know as soon as possible so that they can prepare for disasters.
Depending on the circumstances of the disaster that is like. If not fatal, it can tell the time is near. But if serious thought to the public know as soon as possible in order to prepare for disasters that.
Depending on the situation of natural disasters? If not serious can tell in time. But if serious should let people know as soon as possible to prepare for a disaster.