Alcatraz Island closed on Wednesday morning because of rough water making it potentially dangerous to dock tour boats and their passengers.
Golden Gate National Parks spokeswoman Alexandra Picavet said that the unusual gusts led park leaders to make this semi-unusual call at 11 a.m.
"We don't make this decision lightly," Picavet said in a phone interview. "We know a lot of people have made plans, but we want to be safe."
Picavet said she couldn't remember the last time Alcatraz Island closed due to wind. While it's not unheard of, she said it is rare. In some seasons, she said, the island might have to be closed once a year at most.
All ticket holders can either can a refund or a new ticket. Picavet said "fortunately," there are plenty of tickets available for the rest of the week.