Storms developing in westward moving wave troughs in the easterlies move toward the west and also with a pole ward component given by an angle of approximately 20 to the right of the axis of the trough looking downstream. The motion of storms developing from preexisting vortices can be extrapolated from the track of these vortices. In the easterlies. .
Storms developing on the eastern edge of polar troughs initially move up the trough. .
Pacific storms forming on equatorial shearlines usually are most active in the southern and southwestern portions at the start and they move slowly northeast. After 1 to 2 days, the influence of the trades becomes dominant and the storms turn back toward a direction ranging from west to north. If a storm is discovered without information as to its past movement and the upper air current, it is best to start it along the climatological mean track and then secure the data necessary to determine the steering current. At present, the most practical prognostic technique used by the tropical meteorologist consists of extrapolating the past movement of the synoptic features on his or her chart into the future. The past track of a cyclone represents the integrated effects of the steering forces acting upon it.