Yes it can. Twenty or so years back, Slidell, Louisiana had 24 inches of rain in a 24 hour period, and that was NOT during a hurricane. Louisiana native living in Baton Rouge at the time. I had occasion to drive through there a day or so later, and on both sides of the Interstate was one sheet of water.
Drudge has a link up now from the National Weather service that claims parts of Louisiana will receive over 25 inches of rain total from this storm.