It seems that the storm was the trigger, this is a mold problem, most likely from botrytis, I am not very experienced being a beginner, but instinctively I would remove the leaves that are rotten or that have mold, be careful not to shake the plant so as not to touch the healthy leaves and not spread the damage, do not throw the leaves in the compost or perhaps in the pot, it could make the situation worse, now improve the air circulation and control the humidity and do a preventive and curative fungicide treatment