 Because of the forces that affect tropical cyclone tracks, accurate track predictions depend on determining the position and strength of high- and low-pressure areas, and predicting how those areas will change during the life of a tropical system.The deep layer mean flow, or average wind through the depth of the troposphere, is considered the best tool in determining track direction and speed.If storms are significantly sheared, use of wind speed measurements at a lower altitude, such as at the 70 kPa pressure surface ( above sea level) will produce better predictions.