Heat Wave Map Across U.S. From NOAA

Unhealthy levels of heat and humidity are encompassing much of the eastern half of the U.S., according to NOAA's National Weather Service, as a persistent heat wave continues its grip on the central U.S. while expanding into the East.

According to NOAA's National Weather Service, approximately 995,000 square miles and 150 million people in the United States are under a heat alert (Excessive Heat Warning or Watch or Heat Advisory) as of Wednesday morning.

Temperatures in the 90s to near 100 degrees will feel as hot as 115 degrees or higher when factoring in the high humidity. Record high temperatures are likely to be set in some locations — adding to the more than 1000 records that have been set or tied so far this month.

“This heat is dangerous on many levels,” said Jack Hayes, director of the National Weather Service. “Temperatures and humidity levels are high, the heat will be prolonged, and very warm temperatures overnight won’t provide any respite. All of these factors make this an unhealthy situation.”

Video: This animation shows the predicted daily high temperatures from NOAA's high resolution North American Model (NAM) from July 13-21, 2011.