The USA was really hot on September 15 ... in 1927 and 1936

The heat was widespread on September 15, 1927.

Texas 106, 
Georgia 105, 
Mississippi 105, 
Kentucky 103, 
Alabama 102, 
Illinois 102, 
Tennessee 102, 
Arkansas 101, 
Indiana 101, 
Iowa 101, 
South Carolina 101, 
Virginia 101, 
North Carolina 100, 
Oklahoma 100, 
Pennsylvania 100
Missouri 99, 
Ohio 99, 
Arizona 98, 
Florida 98, 
Wisconsin 98, 
Kansas 97, 
Louisiana 97, 
Maryland 97, 
Michigan 97, 
Nebraska 97, 
Colorado 95, 
Delaware 95, 
New Jersey 95, 
West Virginia 94, 
California 92, 
New York 92, 
South Dakota 92, 
Minnesota 91

 Temperatures on September 15, 1939

Indiana 106, 
Missouri 106, 
Arkansas 105, 
Illinois 105, 
Iowa 104, 
Kansas 104, 
Oklahoma 104, 
Nebraska 103, 
Tennessee 103, 
Louisiana 102, 
Ohio 102, 
Texas 102, 
Wisconsin 102, 
Kentucky 101, 
Mississippi 101, 
Michigan 100, 
Minnesota 100
New York 98, 
South Dakota 98, 
West Virginia 98, 
California 97, 
Pennsylvania 96, 
Arizona 95, 
New Hampshire 94, 
North Dakota 94, 
Florida 93, 
Vermont 93, 
North Carolina 92, 
New Mexico 91, 
South Carolina 91, 
Virginia 91, 
Alabama 90, 
Georgia 90, 
New Jersey 90