Which condition can potentially lead a vessel to capsize?

A vessel's stability is significantly impacted by how it reacts to external forces and loading conditions. Heavy weather, characterized by strong winds and large waves, can lead to an increased angle of heel. When a ship heels excessively due to these conditions, its righting moment (the force that returns it to an upright position) diminishes. If the heel angle becomes too steep, the ship may reach a point of no return where it cannot recover, leading to capsizing.

In contrast, conditions like moderate weather create less stress on the vessel, while excessive ballast weight, though potentially dangerous, usually results in a lower center of gravity that can stabilize a vessel, assuming it is within safe limits. Even weight distribution further enhances stability by ensuring that the ship responds predictably to external forces. Thus, heavy weather increasing heeling constitutes a direct and significant risk to a vessel's stability, making it the correct choice in identifying a potential cause for capsizing.