i believe that. you are getting closer to the sub tropical climate, depending on the wind and time of the year the avarage temperature is warmer there.
Well, it doesn't matter if it's yours or your friend's. You can advertise forums in your signature or if it comes up in normal conversation with people you know who have actual reason to care about your forum, and that's pretty much it.
By definition, you are annoying people if you randomly ask them to join a forum. If they're a friend of yours or something and you have good reason to think beforehand that they'd specifically be interested to know that you made a forum, you can tell them, but messaging random people to advertise is spam.