The newly designated depression began to track west-northwestward over Cuba, which is known to disrupt tropical cyclone development.

Quick organization occurred, and a day later, the system was given a high chance of tropical cyclone development within 48 hours.

Since the upper-level wind had not yet become conducive for tropical cyclone development, the system remained disorganized throughout the day.

As conditions became increasingly favorable for tropical cyclone development, Helene began to rapidly intensify.

A second competing theory for extratropical cyclone development over the oceans is the Shapiro-Keyser model, developed in 1990.

Although Grace was over waters normally not warm enough for tropical cyclone development, low wind shear allowed the convection to persist.

Post-analysis revealed that this tendency was an indication of tropical cyclone development.

Although a powerful storm, it quickly weakened as conditions became hostile for tropical cyclone development.

The depression tracked generally southward, soon encountering a more favorable environment for tropical cyclone development.

By September 18, the disturbance entered a region where there was sinking air, an inhibiting factor of tropical cyclone development.