The $1.00 will probably be a test transaction to make sure the card actually works. This is likely because they won't charge you for the actual subscription amount until your subscription expires (tomorrow from what you wrote) so this is sort of standard practice for companies that are going to be charging the card later so they can confirm now if it works or not and more importantly tell you that there's a problem (if they try to take it later and it fails obviously they can email you etc, but you might not read it for hours/days and right now they know you are right there so it makes sense to test it knowing this).

Usually test transactions get instantly refunded so you don't actually get charged anything which I think is probably what will happen here, but I have seen some companies simply knock off that value from the main charge when that happens so SE might do that since it's tomorrow you're due to renew.