I have the small Planet Waves humidifiers that fit in the guitar strings and I use them year round in theses parts. It's a bit better in the summer, but still dry.
I have multiple hygrometers and use a NOMA that has about a 2 gallon tank on it. I mostly just humidify one room (the one with the acoustic guitars in it). I dehumidify with a central air conditioning system when the weather gets to the 'too much' point.