As shown above, a decision arc is a tool that shows, graphically, the point when certain decisions are made or actions initiated.  For example, if a storm is moving at 10 MPH towards a location and an action point is triggered by the arrival of 34 knot winds in 16 hours, then a "circle" is drawn around that location at a distance of 160 miles.  When graphically, the area of 34 knot winds "intersects" with the arc, that action point checkpoint has arrived.

On a static tracking chart, the user is presented with the option of either accepting the storm's forecast speed of motion and intensity or to override it.