This article says that 64 is the normal average temperature for Sept. 3. In fact, that is normal average temperature for Oct. 3.
Weather for September 2010 hottest on record since 1980
September ended with record torrents of rain that may have washed away memories of one of the distinctive aspects of the month. It was one of the hottest Septembers in Washington history, continuing a trend of thermal overachievement that began here months ago.
According to preliminary National Weather Service figures, September's average temperature was 75.5, five degrees above average. That made the month the hottest September since 1980, when the average temperature was 77.1 degrees.
Since record-keeping for Washington began in 1871 (September temperature: 62.3 degrees), it appeared that last month was the fourth-warmest September recorded in the city.
The first three days of October have departed from the precedent set through the summer. The average temperature for Friday, Saturday and Sunday has been at least a degree below normal.
On Sunday, both the high temperature of 67 degrees at Reagan National Airport and the low temperature of 53 were considerably below normal.
As a result, the day's average of 60 degrees fell four degrees below the Sept. 3 average of 64.