Powered or unpowered is really more about the devices you are going to plug into the USB ports...
The USB port supports providing 5 volts to the devices you want to connect, but the current is limited by the capacity of the source (motherboard or other). A powered hub is required when you either have high-current devices such as hard drives and CD drives OR a large enough quantity of USB devices that would exceed the current limits.
Since the Meteohub and Davis are both powered by their own supplies, an unpowered hub should be fine if all you need to add is a thumbdrive or two...