The correct answer is B) vessel motions increase. During a storm, the increased motion of the vessel will cause higher dynamic loads on the mooring lines, which increases the chance of fatigue failure. As the vessel experiences greater pitching, rolling, and surging motions, the mooring lines are subjected to higher cyclic stresses, leading to a higher risk of fatigue failure. The other options are incorrect because: A) Increasing the vertical center of gravity (KG) would generally increase the vessel's stability, not the fatigue failure risk. C) Decreasing the KG would have the opposite effect, improving the vessel's stability and not increasing the fatigue failure risk. D) Decreasing the mooring tensions would actually reduce the risk of fatigue failure, not increase it.