The area at risk for tornadoes on Wednesday includes Chicago, but the threat is most likely away from the city and east of Lake Michigan, Mr. Lyons said. St. Louis, which experienced a deadly tornado outbreak last month, is also under some risk, but the conditions are expected to be different and far less severe than what they were then, he said.

Erick was upgraded to a hurricane on Wednesday morning. Additional rapid strengthening is feared prior to approaching the southwestern coast of Mexico on Thursday with the effects of a major hurricane.