Volunteers splash water on runners at the Army Ten-Miler to keep them cool Sunday. (John Sonderman via Flickr)

No matter the time of day, it felt like a sauna walking outside in the Washington area Sunday.

The temperature never fell below 75 degrees, a first for the month of October. This 75-degree low broke the record for October’s warmest low of 74, set in 1898 and tied in 1941. Records date to 1871.

Whether it was early in the morning or late at night, the temperature remained above the normal high for the date (Oct. 8), which is 71 degrees.

It was also abnormally humid. The thick, tropical air surged north Saturday as Hurricane Nate made landfall along the northern Gulf Coast. By Saturday night, humidity levels were high even by midsummer standards.


GFS model simulation of precipitable water, a measure of atmospheric moisture between Saturday morning and Sunday evening.

While October postseason baseball is normally played in crisp autumn air, Nationals Park was consumed by a muggy air mass more typical of mid-July as the Nationals took on the Cubs on Saturday night.

“I can’t even remember a summer night feeling that oppressive,” tweeted @DC4Hope, reporting on her experience at the game.

The dew point, which is a measure of humidity, hovered between 74 and 76 degrees Sunday. The sultry conditions made running in the Army Ten-Miler difficult to bear. “It was brutal,” tweeted Rudy Alvarez.

Whenever the dew point exceeds 70 degrees, it’s uncomfortably humid. Over 75 degrees? That’s entering oppressive territory.

Capital Weather Gang information lead Ian Livingston tweeted that such humidity levels are “basically unheard of” at this time of year:

Washingtonians were having none of it and expressed their displeasure on Twitter:

In addition to Washington, Dulles also had its warmest October low Sunday, falling only to 73 degrees, four degrees higher than the previous record of 69 (set Oct. 4, 1986 and Oct. 7, 2005).


(National Weather Service)

The Washington region wasn’t alone in experiencing abnormally warm lows and high humidity.

Philadelphia also had its warmest minimum temperature on record during October, with a low of 74.

In Miami, the low Sunday fell to only 83 degrees, its highest so late in the year.

On Monday, the warm, humid air continued to hover over the Washington region. The dew point registered 75 degrees through midday and was only expected to slowly fall through midweek.