Don't know exactly where it is on your particular model but there should be a short rubber pipe under your car or at the back of the engine bay low-down, this is to run-away the moisture (water) that your air-con removes from the air going into your cabin, this is all part of the cooling process and nothing to worry about.
The more humid the air, the more moisture is removed, so it is more noticeable in muggy weather.
Other cause could be leaking fluid of some kind but you would have had warning alarms of some kind to off by now.