KINGSTOWN, St. Vincent—Conditions worsened on Sunday at a volcano on the eastern Caribbean island of St. Vincent as loud rumbling, lightning and heavy ashfall were observed and residents reported power cuts. The eruption Friday of La Soufrière forced many residents to evacuate their homes, though some remained in place. The rumbling was heard in the capital of Kingstown, about 20 miles (32 kilometers) south. “I’m just here wondering when it’s going to calm down,” resident Kalique Sutherland said. Lava has begun to flow from the volcano, said Prof. Richard Robertson, the lead scientist at the University of the West Indies Seismic Research Center. “It’s likely that at some point it would quiet down and hopefully we would have a break so that we could recover a little bit more, but don’t be surprised if after the break it picks up like this again,” Robertson said. Elford Lewis, a 56-year-old farmer …