Saturday
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 24 2010 was a Tuesday.
August 31 2010 was a Tuesday.
August 13 2010 was a Friday.
August 20 2010 was a Friday.
August 7 2010 was a Saturday.
August 1 2010 was a Sunday.