It was a Friday.
This varies from year to year. The 13th, August, 2010, is a Friday.
It can fall on any day
August 1, 2010 was a Sunday.
August 23 2010 was a Monday.
August 5 2010 will be a Thursday.
August 1 2010 was a Sunday.
August 15 2010 was a Sunday.
August 22 2010 was a Sunday.
August 29 2010 was a Sunday.
August 2 2010 was a Monday.
August 9 2010 was a Monday.