The cyclone phase space represents an rare example of how the development of research occurred simultaneously with its implementation into operations, although primarily in an experimental manner until recently. For key storms in the 2001-2003 hurricane seasons, the structural guidance provided by model-forecast cyclone phase diagrams will be presented, along with the corresponding verification provided by model analysis and multi-model consensus. It will be shown how the cyclone phase diagrams have lead to improved anticipation of structural change and transition. Within the presentation, a discussion of the insight into structural evolution for each of the key cyclones in the three seasons will be presented.