No they haven't booked a a nice cabin by the lake only to be greeted by the blade of a hockey masked fiend.
But maybe they are avoiding stepping on crack to avoid breaking their mothers back. Turning around if a black cat crosses in front of them. not walking under a ladder, which regardless of superstition is weird in itself, not exactly safe to do on any day if someone is on it. not putting up an umbrella indoors, maybe turn off the sprinklers.
Forgetting the fact they are witches so are superstitious anyway.
Who believes in the superstition of Friday the 13th more?
Willow - Maybe its like the Bermuda triangle and there's data to back up the craze of misfortune on the date.
Tara - Has a sixth sense about things perhaps it flares up every Friday 13th.
Neither believe - Its just a date on the calendar, they see bad stuff everyday.
Equally believe - They see bad stuff everyday but nothing quite like what they see on Friday 13th.
I have a different opinion! - Please say in comments.
Ill go Tara. Even if there is nothing to it she will likely pick up on the unease of the people around her due to the day and that in itself is cause to believe something bad will happen.
I think Willow would try to brush something off and rationalise it with something else as a coping mechanism, rather than believe in the Friday 13th superstition.