This U-28A is a Pilatus PC12/45 (c/n 646) built in 2005 and registered as N875RJ. The U. S. Special Operations Command acquired it and converted it to a U-28A with number 08-0646. This aircraft was possibly in the Miami area due to a SOCOM military realistic urban exercise with federal and local civilian law enforcement agencies that involved at least several Black Hawk helicopters and other aircraft.

The U. S. Special Operations Command headquarters is located on MacDill AFB, Florida. More information about the USSOCOM is at: http://www.socom.mil/Pages/AboutUSSOCOM.aspx
and http://www.americanspecialops.com/photos/usaf/U-28A.php