I don't know. I know this was something we could do in Sims2. And I do know that with each new game save we can specify which season we want to start off with, but I see no way to adjust the seasons in each neighborhood. Perhaps, someone who knows more may come along and clarify.
On Sulani, it only gets cool/cold at night. Even in winter, you get warm days. It rains more, but if I can't deal with the rain I just stop it with the weather cheats or have my merman change it.