Warm tongue steering of tropical cyclones

R.H. Simpson in his article "On the Movement of Tropical Cyclones" states that by using charts of the difference in height between the 700 mb. and 500 mb. levels (mean virtual temperature charts), it has been found that a tongue of warmer, lighter air is associated with the moving storm. This tongue is orientated with its major axis parallel to the movement of the cyclone. An excellent lag correlation exists, such that the orientation of the tongue at any instant usually indicates the direction of cyclone movement for the ensuing 24 hour period. It is proposed to test the application of R.H. Simpson's theory to Australian Tropical Cyclones.