Why is thirteen considered unlucky? Is it Biblical?
Judas was the thirteenth member of the group seated at the Last Supper. Thirteen steps up the gallows (7 1/2 to 8 inches each gives a killing drop). Loki, considered the 13th Norse god is responsible for mischief. Friday the thirteenth costs businesses billions of dollars in trade (which I am assured they make up on the 14th, 15th and 16th). Some buildings omit the thirteenth floor.
But thirteen is the very best number in other contexts. It is the age of Bar Mitzva. In a deck of 52 cards, each suit contains 13 cards. In Italy "fare tredici" means hit the jackpot. It is the best day of the month to fly because of the vacant seats.
Triskaidekaphobia has little scientific support other than psychologists noting that those who fear the thirteenth may be distracted by their fear and prone to error.
Scientific or not, 2017 hosted an active hurricane season for the US gulf and east coasts.