Disable the "None of your preferred networks are available" dialog on OS X

• Open the Network pane of the System preferences.
• Select AirPort in the list on the left.
• Uncheck the “Ask to join new networks” checkbox.
• Et voilà! :)

There are two options that I could see that might work for you Uncheck ask to join new networks and try unchecking show wifi status in bar. These are options available in the Network Preferences. You could also try to set the wifi service to inactive. Click the service cog at the bottom left while the wifi service is selected.

If all else fails just turn the wifi off. I assume you aren't using it since you want to disable the warnings and you know its not connected.