Guidelines for Forecasting the Interaction of a Tropical System with a Baroclinic Through

These guidelines have been developed from the study of several trough/tropical system interactions off the east coast of North America.

1. Diagnose any baroclinic troughs that could potentially interact with the tropical system. Note their characteristics: speed; direction of movement; diffluent/confluent; tilt.  

2. Estimate when the 500mb vorticity maximum associated with the tropical system first encounters the strengthening 500mb flow east of the approaching baroclinic trough.  

3. The beginning of the extratropical transition process (ET) can be considered the approximate time the tropical system becomes absorbed into the 500mb stream.
 
4. The speed of the transitioning storm can be estimated by taking 3/4 of the geostrophic wind at 500 mb early in transition to 1/2 late in the transition process.
 
5. Deepening of the transitioning system is likely to begin when the approaching baroclinic trough axis moves to within 5° latitude of that system.
 
6. The direction of motion of the transitioning system is approximately the same direction as the 500mb wind before deepening and approximately 25° cross-contour towards lower heights during the deepening period.