Yes you can use DateFormatter (without NS in Swift 3, the same applies for Date not NSDate). To properly parse your date string you need to use the date format "MMMM dd, yyyy"
and set the date formatter locale to "en_US_POSIX"
let string = "December 20, 2016"
let formatter = DateFormatter()
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.dateFormat = "MMMM dd, yyyy"
if let date = formatter.date(from: dateString) {
print(date) // "2016-12-20 02:00:00 +0000\n"
formatter.dateStyle = .short
let stringFromDate = formatter.string(from: date) // "12/20/16"
}