I was there for a week last November. If you stay in Naha I highly recommend you rent a car so that you can get out of the city and travel around. I found Okinawa drivers very courteous, polite, and safe so I had little difficulty adapting to driving on the ''wrong'' side of the road. The speed limit is 40 km/h in the city and on the smaller highways outside Naha and is 80 km/h on the expressway (toll highway).
Weather wise, it was quite warm and it did rain. In fact my rental car and a quite a few other cars in the Okinawa world parking lot got flooded when the storm drain got clogged (so I suggest if you rent a car take any and all insurance they offer...even the optional insurance). But even with the rain there is plenty to see and do.
If you are there around the 15th of November watch for children visiting shrines for Shichi-Go-San. They are so cute in their kimonos.
Great ice cream store on Kokusai Dori that sells soft-serve mango ice cream. Delicious.
If you are interested you can see pictures of my visit to Okinawa on my blog here: