The official 24-hour rainfall record for the state of Virginia is 14.28 inches observed at Williamsburg on September 16, 1999 is a result of Hurricane Floyd. The extreme rainfall produced by Floyd caused widespread flooding on larger rivers and tributaries; including setting a new record flood stage on the Nottoway River near Sebrell, VA. Smaller streams and creeks also experienced flash flooding.
The unofficial 24-Hour rainfall record for Virginia is 27.35 inches in Nelson County, VA on August 20, 1969. The rainfall was associated with the remnants of Hurricane Camille and is one of the most disasterous floods on record in Virgina. Read this report from NOAA for more information about this event.