, June 30 -- A powerful heat wave is expected to grip much of the central and eastern United States this week, bringing dangerously high temperatures to several cities hosting FIFA World Cup knockout matches and raising concerns for both players and fans.

Forecasters say a strong heat dome will push temperatures and humidity to uncomfortable levels, with the heat index, or the "feels-like" temperature, expected to climb above 100 degrees Fahrenheit (38 degrees Celsius) in several areas. Open-air stadiums in cities including Boston, Philadelphia and Kansas City are expected to be among the hardest hit.

"This week is going to be extremely hot," said Geoff Cornish, assistant chief video meteorologist at AccuWeather. He described it as a ma...