Northeast heat wave promises a scorching July Fourth

July 2 (UPI) -- The heat wave in the Northeast will continue through the Fourth of July holiday, forecasters say.

Temperatures Washington, D.C., Philadelphia, New York City, Hartford, Conn., and Albany, N.Y., have been about 20 degrees above average for four days.

The wave is expected to last through Thursday. Temperatures should then cool briefly this weekend before climbing again above average for the rest of July, forecasters said.

The heat index -- what the weather feels like with humidity -- has reached near 100 or more, prompting heat advisories and excessive heat warnings for more than 60 million people from North Carolina to Maine.

Heat indexes from 100 to 107 are considered dangerously hot.

Washington, D.C., alone reached an index near 105 Monday, as actual temperatures hit the mid- to upper-90s.

Forecasters say the heat on the asphalt or concrete can be particularly dangerous -- possibly over 140 degrees in some areas.