Controlling the humidity in a bathroom

I want to control the humidity in a bathroom. I can setup a simple function where there is min and max humidity e.g. (75 & 82) setting and if the current humidity falls withiabove the range the exhaust fan turns on and when it falls below the range it turns off. However, is the ambient (outside) humidity is within the range (a storm comes through) and the humidity stays within the range the exhaust fan will continue to run until the storm passes and the humidity drops below the range. The exhaust fan will also turn on if a storm comes through and exceeds the max (e.g. 82) and as above will continue to run until the storm passes. So even if the shower has not been used.

Does anyone have an example of how this situation can be handled?