I have gone to Orlando(from Pittsburgh) the past 5 mid Novembers. Every year with the exception of last year(which had temperatures colder than it had been in 40 years) had many days of very warm swimmable weather. The evenings do get cool, but you will be out of DC by nightfall. We are going Nov 16th. We are in Orlando till the 19th, so if the weather looks bad on the 16th, I will try to make my one free change to a better weather day that week.