Lost Souls that aren't rescued before reaching their destination create a Soul Storm on the location, filling it with emotional energy. The story also can force these to occur.
Once a Soul Storm occurs, it remains until you clear it by finishing a scene at that location. Soul Storms block story progression—you can't meet a friend for a chat there while a storm is raging!
Souls Storms also affect the gameplay at their location. During a Soul Storm, instead of having several items to find at once, you have to find your items one at a time.