Hot spots like the East Coast, Mid-Atlantic and the Midwest have all seen their summers hotter than the rest of the country.
The summer heat index has risen to the highest level in more than a decade.
The heat index, based on the National Oceanic and Atmospheric Administration, has climbed to nearly 100.
The national average for July is 85.
In many places, the temperature has reached as high as 101 degrees, according to the National Weather Service.
The hottest year on record was 2003, when the heat index topped 105.
A record high of 99.9 degrees was set in August 2015 in Hawaii.
A temperature record of 100 was set last year in Hawaii and the heat in the Gulf Coast states of Florida, Alabama, Mississippi and Louisiana, among others, was also on the high side.
The National Weather Services is now predicting the heat will continue to increase through next week and could reach the mid-90s for the second time in a week.
The forecast was issued Wednesday by the National Centers for Environmental Prediction.
The agency said the heat may continue to rise across much of the U.S. by Thursday.
Temperatures at the surface in most of the states hit a record high Wednesday and the mercury rose to a record low Thursday in the Chicago area.
The mercury hit 106 degrees Wednesday in the suburbs of Chicago and New York City, according the National Climatic Data Center.
Temperatures were in the 90s in the Midwest, and in the lower Midwest.
In some parts of the South and East, the heat was more extreme.
In the Upper Midwest, the record-setting temperatures were recorded in the Twin Cities area and in Duluth, Minn., where the mercury reached 102 degrees Wednesday.
The temperature in the state dipped to 107 degrees in Duluzela, Minnetonka, about 70 miles north of Minneapolis, on Thursday.
Heat Index: July 2015Temperature: 102 degrees (Fahrenheit)In Minnesota, the mercury dipped to 105 degrees at 4 p.m. local time Thursday, a record-high temperature.
Temperature in the Lower Midwest dropped to 107, and the Northwest and Midwest were all above 90 degrees.
The heat index was calculated by combining the National Climate Assessment and the National Heat Intensity Map, which is based on satellite data.
The data is not perfect and is subject to change.
The National Weather Servers are not part of the NCDC, but the NWS is.
The NWS does release its daily average and daily extreme heat index for the entire country.