With the first tropical storm would-be-hurricane heading towards Florida, I asked the question: "Why is a storm a hurricane when it reaches 74mph?"
I thought maybe it had to do with someone starting with kilometer measurements and then converting it to miles for us silly Americans. But no, 74mph = 119.4km so that can't be right. So somebody... tell me where this came from? Why 74 and not 70 or 80?