The evolution of a tropical wave into a tropical cyclone is dependent on a number of factors. Though these factors interact nonlinearly, much insight can be gained by examining each individually. Pre-storm environmental water vapor variability is shown to impact cyclogenesis over a variety of time and spatial scales. The NVAP dataset is used to show that interannual variability in cyclone activity is influenced by anomalous large scale precipitable water (PW) values. The environmental moisture acts as a necessary, though not sufficient, condition for tropical cyclone development. Also, seasonal increases in PW proceed the annual peak in tropical cyclone activity. In addition, environmental moisture values increase in the vicinity of developing tropical cyclones during the period proceeding depression stage formation.

The spatial evolution of PW during cyclogenesis can also be described using NVAP data. During the three days immediately proceeding depression formation, anomalous moisture transforms from a pattern associated with a tropical wave transversing the open Atlantic Ocean into a symmetric cyclone-like pattern. During this transformation, moisture from both the wave itself and the surrounding environment is transported toward the core of the disturbance. This moisture is used to fuel the disturbance during this significant period of organization. The availability of layered NVAP data makes it possible to described vertical changes in moisture as well. These results indicate that a transverse circulation is present in the disturbance prior to formation of the depression stage. Therefore, it is evident that the primary structures of the evolved tropical cyclone are created during its transformation from a wave to a depression.