safe? sure.. you might be a little cold, but go for it... everyone has a different tolerance for cold, so where one person might not be able to take it, the next might love it. people are jumping in the water here with nothing but board shorts (62-4 water temp).. and i'm pretty sure my balls would break the sound barrier jumping up into my throat if i jumped in with no suit.
so put your suit on, get out there and jump in.. the worst that will happen is you will be cold. bring some dry warm clothes to change into.