There is no exact science. Many experts have spent many hours or more creating models and computer software to input data for the computers to analyze. Wind Speed, weather in other areas, cold fronts, and many other things I have no clue about. Nature is unpredictable. It is not that these people and models are inaccurate or that they don't know what they are doing. It is that no one has a crystal ball. The main point is to give people notice so they can prepare and try to save their lives, the lives of those they love, and their property. They make it very clear that there is no guaranty. Be thankful they are there or we would wake up in the middle of a storm, or worse, be miles from home when it hits us unprepared.