Doyle Rice

USA TODAY

Nights provided no relief from the heat this summer: While days were certainly hot across the USA, it was the endless parade of sultry, swampy nights that set an all-time record.

The summer of 2016 recorded hotter nights than any summer since records began in 1895, according to data released Thursday by the National Oceanic and Atmospheric Administration.

The national average low temperature rested at a balmy 60.8 degrees, about 2.4 degrees above average, said climate scientist Jake Crouch of NOAA's National Centers for Environmental Information. Meteorologists define summer as the year's warmest months of June, July and August.

The reason for the nighttime swelter, especially in the East, was unusually high levels of humidity due to a persistent flow of moisture-laden air off the Gulf of Mexico and Atlantic Ocean, Crouch said. Temperatures don't drop as much at night when the atmosphere is humid.

The devastating flooding in West Virginia in June, Ellicott City, Md., in July and Louisiana in August were also related to the flow of warm, humid air, Crouch said.

Overall, when day and night temperatures were factored in, the summer of 2016 tied with 2006 for the fifth-hottest summer on record in the U.S. Only the summers of 1936, 2012, 2011 and 1934 were hotter, NOAA said.

Three states — California, Rhode Island and Connecticut — were record warm this summer. No state saw a cooler-than-average season.

Several big cities, including New Orleans, Detroit, Cleveland, Las Vegas, Columbia, S.C., and Portland, Maine, also endured their hottest summers.

Eight states in the Mid-Atlantic and Northeast experienced a record warm August, NOAA said. Those included New York, Pennsylvania, Maryland, Delaware, New Jersey, Connecticut, Massachusetts and Rhode Island.

So far for 2016, the U.S. is experiencing its third-warmest year on record.