Millions of Americans will spend the weekend hot under the collar as soaring East Coast temperatures and stifling humidity slapped excessive weather warnings on New York and Philadelphia.
The combination of heat and humidity would make it feel as hot as 110 degrees Fahrenheit (43 degrees Celsius) in the two cities.
Temperatures would stay in the mid 90s until Sunday, with the humidity pushing heat index values higher in New York and Philadelphia, home to around 10 million people combined, meteorologists said.
Authorities warned of heat-related health problems, especially for the elderly and those with chronic health problems and for people who work outdoors.
Americans were advised to stay inside and use air conditioning where possible, check on vulnerable friends and neighbors, drink plenty of fluids to stay hydrated, and not leave children or pets unattended in vehicles.
Overall, the heat wave stretched from southwest Ohio to western Virginia and Washington, and north through Philadelphia, New York and Boston, said David Roth, a meteorologist with the National Weather Service.
Dallas, Washington, parts of New Jersey and New York's Long Island could hit record highs, Roth told AFP.
Five other spots stretching from Maryland's Ocean City to Connecticut might set similar records on Saturday, before the heat fades Sunday and Monday, he added.
