When /tmp/wifi-*.log will show up and how can I stop it?

At least on macOS Sierra (10.12):

1. You can see what WIFI related components have debug logging enabled with:

   /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport debug
   

2. You can disable all debug logging with:

   /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport debug -AllUserland -AllDriver -AllVendor
   

For whatever reason, the debug logging flag was enabled for 'DriverWPA' on my machine and that resulted in /tmp/wifi-{date}__{time}.log files getting generated when joining new WPA2 protected WIFI networks.

On macOS Mojave (10.14.1), hold onto Option and then click the Wi-Fi menu item and then select “Disable Wi-Fi Logging.” That did the trick for me.